test(offline): mock e2e for a device-local vs_ai game (C8)

A Playwright spec drives the whole offline flow in the mock build: force the
installed-PWA display mode, enter offline via the Settings toggle (its readiness check
fetches the dawgs), assert the blue chrome + online-games-hidden + Stats-disabled, then
create and play a device-local English vs_ai game with a pinned bag seed (deterministic
rack NEWYMAO) -- play the opening WAY across the centre, watch the robot reply with a
real move, and reload to confirm the IndexedDB replay.

Enabling infra (all e2e-only; nothing enters the production build):
- mock/client.ts fetchDict serves the per-variant dawgs from the preview build's
  /e2edict/ (was: threw 'unsupported in mock').
- scripts/e2e-dict.mjs copies the real dawgs into dist-e2e from E2E_DICT_DIR (the ui CI
  job fetches the scrabble-dictionary release like the Go jobs; local default: the
  sibling scrabble-solver/dawg); playwright.config runs it between build and preview.
- localgame/id.ts setForcedSeed + gateway.ts window.__mock.setLocalSeed: a mock-only
  seam to pin a local game's bag seed (tree-shaken from prod).
- ci.yaml ui job: fetch the dawgs + pass E2E_DICT_DIR to the e2e step.
- docs/TESTING.md: the offline e2e + the mock-dawg wiring.

Verified: check 0 / unit 482 / e2e 198 (both engines) / app entry 113.8/114.

ui/playwright.config.ts

@@ -21,8 +21,11 @@ export default defineConfig({
     // under /app/ and /telegram/): served from the preview root, an absolute base keeps assets at
     // /assets/ so the SPA-fallback also boots a subpath like /telegram/. Base only prefixes asset
     // URLs, so the minified JS under test is identical to the contour's.
+    // After the mock build, copy the real per-variant dawgs into the preview output (dist-e2e) so the
+    // offline spec can play a real local vs_ai game; the files are e2e-only (never committed, never in
+    // the production build). Source: E2E_DICT_DIR (CI: the fetched release; local: the sibling).
     command:
-      'pnpm exec vite build --mode mock --base / --outDir dist-e2e --emptyOutDir && pnpm exec vite preview --outDir dist-e2e --port 4173 --strictPort',
+      'pnpm exec vite build --mode mock --base / --outDir dist-e2e --emptyOutDir && node scripts/e2e-dict.mjs && pnpm exec vite preview --outDir dist-e2e --port 4173 --strictPort',
     url: 'http://localhost:4173',
     reuseExistingServer: !process.env.CI,
     timeout: 120_000,