feat(web): Nightjar web app - Plaud-style record/transcribe/summarise UI

A runnable, self-hosted web interface so the whole workflow can be tested end to
end: record or upload audio in the browser, watch it transcribe and summarise,
browse a library, play back, and export.

What changed:
- server/app/store.py: SQLite + on-disk audio storage for recordings (stdlib only).
- server/app/pipeline.py: background task audio -> transcribe -> summarise via the
  existing provider layer, updating status (queued/transcribing/summarising/done/error).
- server/app/main.py: web API - POST upload, list, detail, audio (Range), delete, and
  export (txt/md/srt/vtt/json) - and serves the SPA at /.
- server/app/web/: Plaud-style single-page UI (index.html, styles.css, app.js). Sidebar
  library, in-browser recording (MediaRecorder) + file upload, live status polling,
  audio player, summary (overview/key points/actions), timestamped transcript, exports.
- server/Dockerfile + README: two-minute run instructions (default provider: Groq free
  tier for both Whisper + LLM), and a Docker option.
- config: env prefix switched OPENSCRIBE_ -> NIGHTJAR_ to match the brand and the site
  tutorials; .env.example rewritten with a ready Groq quick-start.
- state/TODO: web app recorded as done.

Why:
- User asked for a Plaud-like web interface to test how it all works. Nothing testable
  existed before (marketing site is a brochure; pipeline was unwired). This delivers a
  real, runnable product demo and effectively lands M5/M6 for the HTTP providers.

Notes:
- Slim by design: AI is offloaded to the configured provider, so no local ML deps needed
  for the demo. Byte-compiles clean; JS passes node --check. Local faster-whisper still
  needs its model (M5) for the fully-offline path.

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

state/TODO.md

@@ -65,6 +65,11 @@
 
 ## Done
 
+- [x] Nightjar web app (Plaud-style): browser record/upload -> transcribe -> summarise ->
+      library, playback, transcript, summary, export. FastAPI + vanilla-JS SPA in `server/`,
+      wired to the provider layer (Groq/OpenAI/Anthropic/local). Runnable demo; this is also
+      the practical landing of M5/M6 for the HTTP providers. Config prefix switched to
+      NIGHTJAR_. (PR: feature/web-app, 2026-07-06)
 - [x] Dev testing + emulation harness - native unit tests (wav/range), Wokwi emulator,
       cppcheck + OpenAPI validation in CI, docs/testing.md (PR #3, 2026-07-03).
 - [x] M2 On-device WiFi + REST API - WiFi/SoftAP + mDNS + config(NVS) + device REST API