Add cancel + progress UI, EngineToggle, and Docker deployment

WorkBreakdown.md

@@ -9,8 +9,17 @@ Legend: `[ ]` todo · `[x]` done · `[~]` in progress
 ---
 
 ## WIP Tasks before usage limit cutoff:
-- [~] Allow users to cancel current transcription.
-- [~] Better user-feedback while transcription is in progress (better than "Listening for the first few words")
+- [x] Allow users to cancel current transcription. — Cancel button on the
+      file line, wired to worker termination (D-018); covers decode, pending
+      model download, and the pass itself. Server-engine cancel is tracked in
+      M6 (needs the M5 EngineToggle first).
+- [x] Better user-feedback while transcription is in progress (better than
+      "Listening for the first few words") — the worker now posts
+      `transcribe-progress` (seconds processed / total, from the streamer's
+      chunk timestamps via the pure `TranscribeProgressTracker`); the UI shows
+      a percent in the heading plus a progress bar with mm:ss, and the file
+      flow's placeholder reads "Processing audio…" (the live wording stays
+      live-only).
 
 ## M0 — Scaffold cleanup & docs (small)
 Current state is the raw `bun init` React template.
@@ -143,7 +152,7 @@ Notes (M4):
       (availability probe for the toggle)
 - [x] `src/lib/engine.ts` — `Engine` interface; `BrowserEngine` (wraps worker) and
       `ServerEngine` (wraps fetch stream) (D-010)
-- [ ] `EngineToggle` component — visible only with a session; persists choice
+- [x] `EngineToggle` component — visible only with a session; persists choice
       (persistence helpers + status probe already in `lib/engine.ts`; remaining:
       the component, lifting `useAuth` out of `AuthForms` into `App` so both see
       one session state, and routing the file flow through the selected engine —
@@ -154,7 +163,7 @@ Notes (M4):
       `Bun.spawn` against `tests/fixtures/fake_sidecar.py`); real inference is
       the opt-in `FW_INTEGRATION=1` test + manual run in `tests/server-engine.md`
       (no pip/browser in the dev environment; same caveat as M2/M3)
-- [ ] Deployment: optional Python/faster-whisper layer for the Docker image +
+- [x] Deployment: optional Python/faster-whisper layer for the Docker image +
       deployer note (base image stays Bun-only; install
       `server-py/requirements.txt` to enable the server engine)
 
@@ -183,11 +192,37 @@ Notes (M5):
 - Smoke-tested live against the dev server: `/` + auth unchanged; status
   401 → (register) → 200 `{available:false, reason:"faster-whisper is not
   installed…"}`; POST → 503 with the same reason, body untouched.
+- EngineToggle: one `useAuth()` lives in `App` (passed into `AuthForms` and
+  gating the toggle); the status probe runs on sign-in and the server option
+  renders disabled-with-reason when unavailable. The file flow now goes
+  through the `Engine` interface for **both** paths (D-010): `BrowserEngine`
+  shares the worker with the live loop (distinct requestId namespaces) and a
+  new `stream` flag on the transcribe message keeps token partials +
+  transcribe-progress flowing for id-carrying engine passes (live passes stay
+  non-streaming). Server runs skip the browser model load, show segment
+  partials without a progress bar (faster-whisper's stream carries no window
+  boundaries), and cancel by aborting the fetch (D-018 amendment) — browser
+  runs keep worker-termination cancel. The choice persists in localStorage
+  but only takes effect while signed in with the engine available.
+- Deployment: multi-stage `Dockerfile` — `runtime` (Bun-only, 244 MB) is the
+  default target so plain `docker build .` (existing CI) is unchanged;
+  `--target with-server-engine` (405 MB) adds python3 + faster-whisper in a
+  venv at `/opt/faster-whisper` (wired via `SIDECAR_PYTHON`), with
+  `FASTER_WHISPER_DOWNLOAD_ROOT` under the `/app/data` volume so weights
+  persist. README.md documents both flavors, all runtime env vars, the DB
+  volume, and the HTTPS/reverse-proxy requirement. Verified live in Docker:
+  Bun-only image degrades per D-013 (`available:false`, "python3 is not
+  available…"); server-engine image ran a real `POST /api/transcribe` of
+  `en_aiproblem.m4a` end-to-end, streamed segments matching the fixture
+  transcript — the server half of the M5 integration-test item is now
+  exercised for real (browser half still needs the manual run).
 
 ## M6 — Hardening & polish
 - [ ] Error taxonomy: unsupported file, out-of-memory (suggest smaller model),
       WebGPU device-lost, network loss mid-download (resume or clear retry)
-- [ ] Cancel in-flight transcription (both engines)
+- [x] Cancel in-flight transcription (both engines) — browser engine via
+      worker termination (D-018), server engine via aborting the
+      `/api/transcribe` fetch (D-018 amendment; landed with M5's EngineToggle)
 - [ ] Export transcript: .txt and .srt (timestamps already available)
 - [ ] Storage management UI: list cached models, per-model delete
 - [ ] Basic a11y pass (keyboard, focus, aria on progress/live transcript)