fix(settings): restore mounted flag on remount so auto-save can settle (#5613)

The auto-save mount effect only cleared `mountedRef` in its cleanup and never
re-set it to true on setup. Under React StrictMode the initial
setup/cleanup/setup cycle therefore leaves `mountedRef.current` pinned to false
for the component's whole life. A successful save then never reaches the
terminal branch (`succeeded && mountedRef.current`), so the status is stranded
on "saving" and the success toast never fires — the settings save indicator
spins forever even though the PATCH returned 200.

Set `mountedRef.current = true` on every mount so the flag reflects the live
component. Shared by all auto-saved settings (repositories, GitHub, etc.).

Add a StrictMode regression test asserting onSuccess still fires.

packages/views/settings/components/use-auto-save.test.tsx

@@ -1,3 +1,4 @@
+import { StrictMode } from "react";
 import { act, render, waitFor } from "@testing-library/react";
 import { afterEach, describe, expect, it, vi } from "vitest";
 import { useAutoSave } from "./use-auto-save";
@@ -53,6 +54,23 @@ describe("useAutoSave success feedback", () => {
     });
   });
 
+  it("still reports success under StrictMode's double-invoked mount", async () => {
+    // StrictMode runs setup/cleanup/setup on mount. A mount effect that only
+    // clears the mounted flag in cleanup leaves it false for the component's
+    // life, so a successful save is silently dropped: neither the "saved"
+    // status nor onSuccess ever fires and the indicator spins forever.
+    const onSave = vi.fn(async () => undefined);
+    const onSuccess = vi.fn();
+    render(
+      <StrictMode>
+        <AutoSaveHarness value="saved" onSave={onSave} onSuccess={onSuccess} />
+      </StrictMode>,
+    );
+
+    await waitFor(() => expect(onSave).toHaveBeenCalledWith("saved"));
+    await waitFor(() => expect(onSuccess).toHaveBeenCalledWith("saved"));
+  });
+
   it("waits for the latest queued value before reporting success", async () => {
     vi.useFakeTimers({ shouldAdvanceTime: true });
     const first = deferred<void>();

packages/views/settings/components/use-auto-save.ts

@@ -131,13 +131,16 @@ export function useAutoSave<T>({
     };
   }, [delay, enabled, isEqual, runSave, value]);
 
-  useEffect(
-    () => () => {
+  useEffect(() => {
+    // Restore the invariant on every mount. Under React StrictMode the initial
+    // setup/cleanup/setup cycle would otherwise leave mountedRef pinned to false
+    // for the component's whole life, stranding status at "saving".
+    mountedRef.current = true;
+    return () => {
       mountedRef.current = false;
       if (timerRef.current) clearTimeout(timerRef.current);
-    },
-    [],
-  );
+    };
+  }, []);
 
   return { status, flush, saveNow };
 }