revert(test): abandon shared-mock dedup — infeasible in vitest browser mode

CI proved cross-file sharing of a virtual-module mock body cannot work in
@vitest/browser-playwright 4.1.6: the static-import spread fails the hoist
("no top level variables"), and the await-vi.hoisted-import form fails to
parse ("Unexpected identifier 'vi'"). vi.hoisted has the same hoist
constraint as vi.mock, so there is no way to thread an external module's
body into the factory here.

Reverts Phase 1: restores the 4 $app/forms/$app/navigation specs to their
inline factories, inlines NotificationBell.spec's forms stub, deletes the
src/__mocks__/$app/* modules and the $mocks alias (vite, vitest-coverage,
kit). The no-factory-ban meta-test stays (no-factory vi.mock is still
banned). ADR-012 amended to record the infeasibility. Everything else
($app/state migration, confirm context-inject, notification refactor, the
pin, the meta-test) is unaffected. Part of #560.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/adr/012-browser-test-mocking-strategy.md

@@ -145,16 +145,27 @@ PR #657 attempted to delete `vi.mock` factories entirely and rely on Vitest auto
 
 7. **In-suite no-factory-ban meta-test** at `frontend/src/__meta__/no-factory-ban.test.ts` — same source-scan mechanism as the other meta-tests; fails if any browser spec contains a `vi.mock('mod')` with no second argument.
 
-### Sanctioned dedup: shared mock body + per-spec sync factory
+### Cross-file sharing of a virtual-module mock body is infeasible (the third false premise)
 
-To remove duplicated factory bodies without removing the factory, keep one shared mock module per virtual module under `src/__mocks__/` and import it via the `$mocks` alias into a sync factory:
+The original #560 plan ("Option A") proposed deduplicating the non-trivial interceptor factories by importing a shared body from `src/__mocks__/` into a sync factory:
 
 ```ts
 import * as formsMock from "$mocks/$app/forms";
 vi.mock("$app/forms", () => ({ ...formsMock }));
 ```
 
-The shared module owns any non-trivial mock logic and embeds its own `beforeEach` reset of mutable state, so isolation is structural. The `$mocks` alias is declared in **both** `vite.config.ts` and `vitest.client-coverage.config.ts` so it resolves in the coverage job too. Only genuinely-shared logic is consolidated; the ~80 trivial inline factories (`enhance: () => () => {}`, `{ goto: vi.fn() }`) are left untouched.
+**CI proved this does not work in `@vitest/browser-playwright` 4.1.6**, across two runs:
+
+1. The static-import form above fails at runtime — vitest hoists `vi.mock` _above_ the import, so the factory references an uninitialised binding: `vi.mock factory: make sure there are no top level variables inside, since this call is hoisted`.
+2. The documented escape, loading the body through an async hoisted import, fails to even parse in browser mode — vitest's hoist transform mangles it: `SyntaxError: Unexpected identifier 'vi'`.
+
+   ```ts
+   const formsMock = await vi.hoisted(() => import("$mocks/$app/forms")); // parse error in browser mode
+   ```
+
+`vi.hoisted` has the _same_ constraint as `vi.mock` (its factory can't reference top-level imports either, since it too is hoisted above them), so there is no way to get an external module's body into the hoisted context here. **Therefore: do not share virtual-module mock bodies across spec files. Define each `vi.mock` factory inline, with a synchronous body.** Duplicating the handful of interceptor factories is the accepted cost — it is the only pattern that works. The `src/__mocks__/$app/*` modules and the `$mocks` alias added for Option A were removed. (Revisit on a newer `@vitest/browser-playwright` whose hoist transform handles async `vi.hoisted` imports.)
+
+The no-factory-ban above still stands: every `vi.mock` of a virtual module must pass an _inline_ sync factory — never no factory, never a spread of an imported binding.
 
 ### Rejected: Option C (config-level auto-resolve)