WIP: M3 PWA/offline implementation, M4 auth (backend + frontend), D-013 faster-whisper

- M3: hand-rolled service worker (precache + runtime /ort caching), precache
  manifest injection, SW registration/update toast, manifest + generated icons,
  production build script, offline indicator in ModelPicker (D-005/D-007)
- M4 backend: bun:sqlite users/sessions (D-009), Passport local strategy behind
  connect-compat adapter (D-008), /api/auth routes wired into dev+prod serving,
  Bun.password Argon2id, 38 auth tests
- M4 frontend: AuthForms + useAuth + framework-free authClient, session-aware
  header, anonymous-first fail-silent offline handling, 18 client tests
- D-013: server engine (M5) will use faster-whisper via Python sidecar;
  browser side stays Transformers.js (CTranslate2 has no WASM build)
- bun test: 83 pass / tsc --noEmit clean
- Note: M3 doc closeout (WorkBreakdown/Architecture/tests/offline.md) still in
  flight from a background agent; follow-up commit will finish docs

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

WorkBreakdown.md

@@ -45,16 +45,28 @@ Notes (M1):
   locally.
 
 ## M2 — Model choice + WebGPU (core)
-- [ ] `src/lib/models.ts` — curated catalog with sizes and dtype defaults (D-006)
-- [ ] `ModelPicker` component — size estimates, English-only vs multilingual,
+- [x] `src/lib/models.ts` — curated catalog with sizes and dtype defaults (D-006)
+- [x] `ModelPicker` component — size estimates, English-only vs multilingual,
       downloaded-state badge (query Cache API)
-- [ ] WebGPU detection in worker, `device` selection with WASM fallback (D-004);
+- [x] WebGPU detection in worker, `device` selection with WASM fallback (D-004);
       surface active backend in UI
-- [ ] Handle model switching (dispose old pipeline, load new)
-- [ ] Language / task options for multilingual models (transcribe vs translate)
-- [ ] Verify quantized variants (q4/q8/fp16) on both backends; record working
+- [x] Handle model switching (dispose old pipeline, load new)
+- [x] Language / task options for multilingual models (transcribe vs translate)
+- [~] Verify quantized variants (q4/q8/fp16) on both backends; record working
       combinations in `models.ts`
 
+Notes (M2):
+- Quantized-variant verification is pending manual in-browser testing (no real
+  browser in the dev environment). `models.ts` encodes the community-known-good
+  combinations — WASM: q8 (tiny→small) / q4 (medium, large-v3-turbo); WebGPU:
+  fp32 encoder+decoder for tiny/base (fp16 encoders known-bad there), fp16
+  encoder + q4 merged decoder for small/medium/large-v3-turbo — each with a
+  `verified` flag and note. Only `whisper-tiny.en @ wasm/q8` (exercised in M1)
+  is marked `verified: true`; flip the flags as manual testing confirms each.
+- Downloaded badge (D-005): `src/lib/modelCache.ts` inspects Cache Storage for
+  transformers-cache entries with `.onnx` hits per model id; M3's offline
+  indicator should reuse `getDownloadedModels`.
+
 ## M3 — PWA & offline (core)
 - [ ] `manifest.webmanifest` + icons; installability
 - [ ] `src/pwa/sw.ts` — app-shell precache, cache-first static, network-only API (D-007)