feat(admin): assistant feature-flag toggle panel

New admin slug `assistant` between `ai-quality` (provider config)
and `coach-feedback` (in-app feedback inbox). The panel renders six
`<SettingsToggle>` rows — master plus five sub-flags — and writes
through a dedicated `PUT /api/admin/settings/assistant-flags`
endpoint. Optimistic UI flips on click; failure surfaces a toast
and re-invalidates the read query.

The dedicated endpoint (separate from the generic `/api/admin/settings`
PUT) lets the panel scope its audit trail to a single
`admin.settings.assistant-flags.update` action and lets the
optimistic UI bind 1:1 to a focused request/response shape. The
PUT handler echoes both the raw column values and the resolved
shape so the panel can render the master vs sub-flag distinction
visually.

Sub-toggles grey out when the master is off (UX-wise) so the
operator can see which sub-flags are individually flipped before
unmuting the master. Writes invalidate the runtime
`/api/feature-flags` cache so the operator sees the toggled
surface react within the same session.

i18n: `admin.section.assistant.{title,subtitle}` and
`admin.assistant.*` keys land in all six locales (DE proper, the
five English-leaning admin locales mirror the English copy as is
the established convention for admin strings).

src/components/admin/admin-shell.tsx

@@ -75,6 +75,11 @@ export const ADMIN_SECTIONS: readonly AdminSection[] = [
     titleKey: "admin.section.ai-quality.title",
     icon: Sparkles,
   },
+  {
+    slug: "assistant",
+    titleKey: "admin.section.assistant.title",
+    icon: Sparkles,
+  },
   {
     slug: "coach-feedback",
     titleKey: "admin.section.coach-feedback.title",

src/components/admin/assistant-section.tsx

@@ -0,0 +1,177 @@
+"use client";
+
+import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { Sparkles } from "lucide-react";
+import { toast } from "sonner";
+
+import { useTranslations } from "@/lib/i18n/context";
+import { SettingsToggle, getApiErrorMessage } from "./_shared";
+
+/**
+ * v1.4.31 — operator-side panel for the six assistant feature
+ * flags. The master toggle gates the whole assistant; five
+ * sub-toggles carve specific surfaces (Coach, Daily Briefing,
+ * per-metric status cards, correlation narration, Health-Score
+ * delta explainer).
+ *
+ * UX:
+ *   - Master toggle at the top. When off, the sub-toggles are
+ *     visually greyed out (kept rendered so the operator can see
+ *     which sub-flags are individually flipped before they unmute
+ *     the master) but cannot be flipped via the disabled `<Switch>`.
+ *   - Optimistic flip + server confirm via `useMutation`; failure
+ *     surfaces a toast and reverts the in-flight toggle by
+ *     re-invalidating the read query.
+ */
+
+interface AssistantFlagsResponse {
+  raw: {
+    assistantEnabled: boolean;
+    assistantCoachEnabled: boolean;
+    assistantBriefingEnabled: boolean;
+    assistantInsightStatusEnabled: boolean;
+    assistantCorrelationsEnabled: boolean;
+    assistantHealthScoreExplainerEnabled: boolean;
+  };
+  resolved: {
+    enabled: boolean;
+    coach: boolean;
+    briefing: boolean;
+    insightStatus: boolean;
+    correlations: boolean;
+    healthScoreExplainer: boolean;
+  };
+}
+
+function useAssistantFlags() {
+  return useQuery({
+    queryKey: ["admin", "settings", "assistant-flags"],
+    queryFn: async () => {
+      const res = await fetch("/api/admin/settings/assistant-flags");
+      if (!res.ok) throw new Error("Failed");
+      return (await res.json()).data as AssistantFlagsResponse;
+    },
+  });
+}
+
+function useUpdateAssistantFlags() {
+  const client = useQueryClient();
+  const { t } = useTranslations();
+  return useMutation({
+    mutationFn: async (
+      patch: Partial<AssistantFlagsResponse["raw"]>,
+    ): Promise<AssistantFlagsResponse> => {
+      const res = await fetch("/api/admin/settings/assistant-flags", {
+        method: "PUT",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify(patch),
+      });
+      if (!res.ok) {
+        throw new Error(await getApiErrorMessage(res));
+      }
+      return (await res.json()).data as AssistantFlagsResponse;
+    },
+    onSuccess: (data) => {
+      client.setQueryData(
+        ["admin", "settings", "assistant-flags"],
+        data,
+      );
+      // Bust the runtime `/api/feature-flags` cache so the operator
+      // sees the toggled surface react within the same session.
+      client.invalidateQueries({ queryKey: ["feature-flags"] });
+      toast.success(t("common.saved"));
+    },
+    onError: (err) => {
+      toast.error(
+        err instanceof Error && err.message
+          ? err.message
+          : t("admin.settingsSaveError"),
+      );
+      client.invalidateQueries({
+        queryKey: ["admin", "settings", "assistant-flags"],
+      });
+    },
+  });
+}
+
+export function AssistantSection() {
+  const { t } = useTranslations();
+  const { data } = useAssistantFlags();
+  const mutation = useUpdateAssistantFlags();
+
+  const raw = data?.raw;
+  const masterOn = raw?.assistantEnabled ?? true;
+  const disabledSubs = !masterOn || mutation.isPending;
+
+  return (
+    <div className="bg-card border-border space-y-6 rounded-xl border p-6">
+      <div className="flex items-center gap-2">
+        <Sparkles className="text-primary h-5 w-5" />
+        <div className="text-lg font-semibold">{t("admin.assistant.title")}</div>
+      </div>
+      <p className="text-muted-foreground text-sm">
+        {t("admin.assistant.description")}
+      </p>
+
+      <SettingsToggle
+        label={t("admin.assistant.master.title")}
+        description={t("admin.assistant.master.description")}
+        checked={raw?.assistantEnabled ?? true}
+        onCheckedChange={(checked) =>
+          mutation.mutate({ assistantEnabled: checked })
+        }
+        disabled={mutation.isPending}
+      />
+
+      <div className="border-border space-y-4 border-t pt-4">
+        <SettingsToggle
+          label={t("admin.assistant.coach.title")}
+          description={t("admin.assistant.coach.description")}
+          checked={raw?.assistantCoachEnabled ?? true}
+          onCheckedChange={(checked) =>
+            mutation.mutate({ assistantCoachEnabled: checked })
+          }
+          disabled={disabledSubs}
+        />
+        <SettingsToggle
+          label={t("admin.assistant.briefing.title")}
+          description={t("admin.assistant.briefing.description")}
+          checked={raw?.assistantBriefingEnabled ?? true}
+          onCheckedChange={(checked) =>
+            mutation.mutate({ assistantBriefingEnabled: checked })
+          }
+          disabled={disabledSubs}
+        />
+        <SettingsToggle
+          label={t("admin.assistant.insightStatus.title")}
+          description={t("admin.assistant.insightStatus.description")}
+          checked={raw?.assistantInsightStatusEnabled ?? true}
+          onCheckedChange={(checked) =>
+            mutation.mutate({ assistantInsightStatusEnabled: checked })
+          }
+          disabled={disabledSubs}
+        />
+        <SettingsToggle
+          label={t("admin.assistant.correlations.title")}
+          description={t("admin.assistant.correlations.description")}
+          checked={raw?.assistantCorrelationsEnabled ?? true}
+          onCheckedChange={(checked) =>
+            mutation.mutate({ assistantCorrelationsEnabled: checked })
+          }
+          disabled={disabledSubs}
+        />
+        <SettingsToggle
+          label={t("admin.assistant.healthScoreExplainer.title")}
+          description={t("admin.assistant.healthScoreExplainer.description")}
+          checked={raw?.assistantHealthScoreExplainerEnabled ?? true}
+          onCheckedChange={(checked) =>
+            mutation.mutate({
+              assistantHealthScoreExplainerEnabled: checked,
+            })
+          }
+          disabled={disabledSubs}
+        />
+      </div>
+    </div>
+  );
+}

src/components/admin/section-slugs.ts

@@ -15,6 +15,11 @@ export const ADMIN_SECTION_SLUGS = [
   "services",
   "integrations",
   "ai-quality",
+  // v1.4.31 — operator-side assistant feature-flag toggles. Sits
+  // between `ai-quality` (provider config) and `coach-feedback`
+  // (in-app feedback inbox) per
+  // `.planning/research/v15-assistant-optional.md` Part B.
+  "assistant",
   "coach-feedback",
   "feedback",
   "reminders",