fix(coach,insights,achievements): honest error states + Plans discoverability

- Achievements: a failed load renders QueryErrorCard instead of falling
  through to zeroed summary tiles and a 'none unlocked yet' empty grid.
- /coach/conversations: a load failure now shows a retry instead of a false
  'no conversations yet' empty state.
- Insights overview error uses the shared QueryErrorCard.
- Coach Plans gains a header cross-link from /coach/conversations (and back),
  a skeleton loading state, and the shared EmptyState primitive.

src/app/achievements/page.tsx

@@ -33,6 +33,7 @@ import { Progress } from "@/components/ui/progress";
 import { Badge } from "@/components/ui/badge";
 import { EmptyState } from "@/components/ui/empty-state";
 import { PageHeader } from "@/components/ui/page-header";
+import { QueryErrorCard } from "@/components/ui/query-error-card";
 import { useAuth } from "@/hooks/use-auth";
 import { useTranslations } from "@/lib/i18n/context";
 import { formatDate } from "@/lib/format";
@@ -271,7 +272,7 @@ export default function AchievementsPage() {
   // alongside `<RecentAchievementsCard>` and
   // `<AchievementUnlockNotifier>` so the three consumers never trigger
   // more than one network call on a cold dashboard mount.
-  const { data, isLoading } = useAchievementsQuery({
+  const { data, isLoading, isError, refetch } = useAchievementsQuery({
     enabled: isAuthenticated && achievementsEnabled,
   });
 
@@ -302,6 +303,21 @@ export default function AchievementsPage() {
     );
   }
 
+  // A failed load must never fall through to the zeroed summary tiles + the
+  // "none unlocked yet" empty grid (UI-STANDARDS §6). Surface an honest
+  // retry instead.
+  if (isError) {
+    return (
+      <div className="space-y-6">
+        <PageHeader
+          title={t("achievements.title")}
+          description={t("achievements.subtitle")}
+        />
+        <QueryErrorCard onRetry={() => refetch()} />
+      </div>
+    );
+  }
+
   const summary = data?.summary;
   const achievements = data?.achievements ?? [];
   const grouped = groupByCategory(achievements);

src/app/coach/conversations/page.tsx

@@ -1,12 +1,14 @@
 "use client";
 
 import { useEffect, useMemo, useState } from "react";
+import Link from "next/link";
 import { useRouter } from "next/navigation";
-import { MessagesSquare, Search, Trash2 } from "lucide-react";
+import { MessagesSquare, Search, Target, Trash2 } from "lucide-react";
 
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { PageHeader } from "@/components/ui/page-header";
+import { QueryErrorCard } from "@/components/ui/query-error-card";
 import { COACH_SCROLLBAR } from "@/components/insights/coach-panel/message-thread";
 import {
   useCoachConversations,
@@ -92,7 +94,8 @@ function groupByRecency(conversations: CoachConversationDTO[]): RecencyGroup[] {
 function CoachConversationsBody() {
   const { t } = useTranslations();
   const router = useRouter();
-  const { conversations, isLoading } = useCoachConversations();
+  const { conversations, isLoading, isError, refetch } =
+    useCoachConversations();
   const deleteMutation = useDeleteCoachConversation();
   const [filter, setFilter] = useState<string>("");
   const [confirmId, setConfirmId] = useState<string | null>(null);
@@ -129,6 +132,16 @@ function CoachConversationsBody() {
               {t("insights.coach.historyTitle")}
             </span>
           }
+          actions={
+            // Surface the sibling Plans ledger — otherwise it is reachable
+            // only from the composer's `+` menu.
+            <Button asChild variant="outline" size="sm">
+              <Link href="/coach/plans" data-slot="coach-conversations-plans-link">
+                <Target className="size-4" aria-hidden="true" />
+                {t("coach.plans.title")}
+              </Link>
+            </Button>
+          }
         />
         <div className="relative">
           <Search
@@ -160,6 +173,11 @@ function CoachConversationsBody() {
           >
             {t("common.loading")}
           </p>
+        ) : isError && conversations.length === 0 ? (
+          // A load failure must not masquerade as "no conversations yet" —
+          // that reads as a data-loss scare and offers no way back. Mirror
+          // /coach/plans and surface a retry.
+          <QueryErrorCard onRetry={() => refetch()} />
         ) : groups.length === 0 ? (
           <div
             data-slot="coach-conversations-empty"

src/app/coach/plans/page.tsx

@@ -1,12 +1,15 @@
 "use client";
 
 import { useEffect, useMemo } from "react";
+import Link from "next/link";
 import { useRouter } from "next/navigation";
-import { Check, Loader2, Target, Trash2, X } from "lucide-react";
+import { Check, Loader2, MessagesSquare, Target, Trash2, X } from "lucide-react";
 
 import { Button } from "@/components/ui/button";
 import { PageHeader } from "@/components/ui/page-header";
 import { QueryErrorCard } from "@/components/ui/query-error-card";
+import { EmptyState } from "@/components/ui/empty-state";
+import { Skeleton } from "@/components/ui/skeleton";
 import { COACH_SCROLLBAR } from "@/components/insights/coach-panel/message-thread";
 import {
   useCoachPlans,
@@ -204,6 +207,17 @@ function CoachPlansBody() {
           <span data-slot="coach-plans-heading">{t("coach.plans.title")}</span>
         }
         description={t("coach.plans.pageDescription")}
+        actions={
+          <Button asChild variant="outline" size="sm">
+            <Link
+              href="/coach/conversations"
+              data-slot="coach-plans-conversations-link"
+            >
+              <MessagesSquare className="size-4" aria-hidden="true" />
+              {t("insights.coach.historyTitle")}
+            </Link>
+          </Button>
+        }
       />
 
       <div
@@ -216,23 +230,22 @@ function CoachPlansBody() {
         {query.isError ? (
           <QueryErrorCard onRetry={() => query.refetch()} />
         ) : query.isLoading ? (
-          <p
-            data-slot="coach-plans-loading"
-            className="text-muted-foreground px-1 py-3 text-sm"
-          >
-            {t("common.loading")}
-          </p>
-        ) : groups.length === 0 ? (
           <div
-            data-slot="coach-plans-empty"
-            className="flex flex-1 flex-col items-center justify-center gap-3 px-6 py-12 text-center"
+            data-slot="coach-plans-loading"
+            className="flex flex-col gap-2"
+            aria-hidden="true"
           >
-            <span className="bg-muted/40 text-muted-foreground flex size-12 items-center justify-center rounded-full">
-              <Target className="size-6" aria-hidden="true" />
-            </span>
-            <p className="text-muted-foreground max-w-xs text-sm leading-relaxed">
-              {t("coach.plans.empty")}
-            </p>
+            {[0, 1, 2].map((i) => (
+              <Skeleton key={i} className="h-16 w-full rounded-xl" />
+            ))}
+          </div>
+        ) : groups.length === 0 ? (
+          <div data-slot="coach-plans-empty">
+            <EmptyState
+              variant="plain"
+              icon={<Target className="size-6" />}
+              title={t("coach.plans.empty")}
+            />
           </div>
         ) : (
           groups.map((group) => (

src/app/insights/page.tsx

@@ -4,7 +4,7 @@ import { Fragment, type ReactNode } from "react";
 import { useQuery } from "@tanstack/react-query";
 import dynamic from "next/dynamic";
 import Link from "next/link";
-import { RefreshCw, SlidersHorizontal, TrendingUp } from "lucide-react";
+import { SlidersHorizontal, TrendingUp } from "lucide-react";
 
 import { useAuth } from "@/hooks/use-auth";
 import { queryKeys } from "@/lib/query-keys";
@@ -20,6 +20,7 @@ import { useScrollResetOnRoute } from "@/hooks/use-scroll-reset-on-route";
 import { useTranslations } from "@/lib/i18n/context";
 import { Button } from "@/components/ui/button";
 import { EmptyState } from "@/components/ui/empty-state";
+import { QueryErrorCard } from "@/components/ui/query-error-card";
 import { Skeleton } from "@/components/ui/skeleton";
 import { cn } from "@/lib/utils";
 import { HeroStrip } from "@/components/insights/hero-strip";
@@ -340,23 +341,11 @@ export default function InsightsPage() {
   // mirroring the <VitalsDashboard> error pattern.
   if (isError) {
     return (
-      <div
-        data-slot="insights-overview-error"
-        role="alert"
-        className="bg-card border-border text-muted-foreground flex flex-col items-start gap-3 rounded-xl border p-4 text-sm sm:flex-row sm:items-center sm:justify-between"
-      >
-        <span>{t("insights.loadError")}</span>
-        <Button
-          type="button"
-          size="sm"
-          variant="outline"
-          onClick={() => refetch()}
-          data-slot="insights-overview-retry"
-          className="gap-1.5"
-        >
-          <RefreshCw className="h-3.5 w-3.5" aria-hidden="true" />
-          <span>{t("common.retry")}</span>
-        </Button>
+      <div data-slot="insights-overview-error">
+        <QueryErrorCard
+          description={t("insights.loadError")}
+          onRetry={() => refetch()}
+        />
       </div>
     );
   }