feat(lists): read and show the list cap on every capped list

Twelve routes answer a capped list with meta.truncated / meta.limit on
the envelope, and the web client read only data, so no surface said a
list had stopped short. apiGetList / apiPostList are now the one client
reader of the cap and ListCapNotice the one line that shows it; every
capped list on the web reads its cap and shows the notice under the list,
the paged readers (side effects, illness episodes) stop on the route's
answer instead of a full-page guess, and the ECG list moves its five
readers onto one hook. The record activity feed sent its cap twice, in
data and on the envelope; it rides the envelope alone now. A guard
derives the capped routes from the tree and binds each to a client that
reads its cap.

src/components/ui/__tests__/list-cap-notice.test.tsx

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+import { describe, expect, it } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+import { I18nProvider } from "@/lib/i18n/context";
+import { readListCap } from "@/lib/api/list-cap-shape";
+
+import { ListCapNotice } from "../list-cap-notice";
+
+const render = (node: React.ReactNode) =>
+  renderToStaticMarkup(<I18nProvider initialLocale="en">{node}</I18nProvider>);
+
+describe("ListCapNotice", () => {
+  it("says the list stopped at its ceiling, with the number", () => {
+    const html = render(<ListCapNotice cap={{ truncated: true, limit: 50 }} />);
+    expect(html).toContain('data-slot="list-cap-notice"');
+    expect(html).toContain("Showing the latest 50");
+  });
+
+  it("renders nothing for a complete list or no cap", () => {
+    expect(
+      render(<ListCapNotice cap={{ truncated: false, limit: 50 }} />),
+    ).toBe("");
+    expect(render(<ListCapNotice cap={null} />)).toBe("");
+  });
+});
+
+describe("readListCap", () => {
+  it("reads the envelope's cap and nothing else", () => {
+    expect(
+      readListCap({ truncated: true, limit: 100, requestId: "r" }),
+    ).toEqual({ truncated: true, limit: 100 });
+    expect(readListCap({ aggregate: {} })).toBeNull();
+    expect(readListCap({ truncated: "yes", limit: 1 })).toBeNull();
+    expect(readListCap(undefined)).toBeNull();
+  });
+});

src/components/ui/list-cap-notice.tsx

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+"use client";
+
+import type { ListCap } from "@/lib/api/list-cap-shape";
+import { useTranslations } from "@/lib/i18n/context";
+import { cn } from "@/lib/utils";
+
+/**
+ * The line under a list the server cut at its ceiling. Renders nothing for a
+ * complete list, so a surface passes the cap it read (`apiGetList`) and
+ * never decides on its own whether to show it. Meta tier: one muted sentence
+ * at the `text-xs` floor.
+ */
+export function ListCapNotice({
+  cap,
+  className,
+}: {
+  cap: ListCap | null | undefined;
+  className?: string;
+}) {
+  const { t } = useTranslations();
+  if (!cap?.truncated) return null;
+  return (
+    <p
+      data-slot="list-cap-notice"
+      className={cn("text-muted-foreground text-xs", className)}
+    >
+      {t("common.listCapped", { count: String(cap.limit) })}
+    </p>
+  );
+}