Add PWA, CLI daemon, deploy tooling, and full documentation

PWA (pwa/):
- Ephemeral QR pairing and trusted device direct reconnect (no QR re-scan)
- Known devices tab as default; pairRoomName() derives deterministic room
- In-app QR scanner via native BarcodeDetector API
- Multi-file send/receive with offer queue and Accept all
- Auto-download on receipt, real-time send/receive progress bars
- Trusted peer nicknames, rename, forget
- Terminal aesthetic: #080808 bg, #00e87a accent, JetBrains Mono
- manifest.json corrected (SVG icon, theme_color, share_target)
- Apple PWA meta tags for home screen install

CLI (cli/):
- flit send / flit recv: ephemeral one-shot transfer with terminal QR
- flit daemon: persistent receiver for trusted peers from ~/.flit/daemon.toml
  - TOML config: signal_url, turn_url, download_dir, [[peers]]
  - One goroutine per peer, exponential backoff reconnect (2s→30s cap)
  - transport.PairRoomName() and Session.OnDisconnected added
- Anchor/TURN config via FLIT_SIGNAL_URL / FLIT_TURN_URL env vars (no hardcoded URLs)

Deploy:
- build-pwa.sh, deploy-pwa.sh / serve-pwa.sh templates in README (gitignored)
- .gitea/workflows/build.yml: PWA build on v* tag, Gitea release artifact
- pwa/public/config.js gitignored; config.js.example committed
- .env.example for CLI env vars

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pwa/public/manifest.json

@@ -4,11 +4,10 @@
   "description": "Ephemeral, end-to-end encrypted file transfer between your own devices.",
   "start_url": "/",
   "display": "standalone",
-  "background_color": "#0d1117",
-  "theme_color": "#1f6feb",
+  "background_color": "#080808",
+  "theme_color": "#00e87a",
   "icons": [
-    { "src": "/icon-192.png", "sizes": "192x192", "type": "image/png" },
-    { "src": "/icon-512.png", "sizes": "512x512", "type": "image/png" }
+    { "src": "/favicon.svg", "sizes": "any", "type": "image/svg+xml", "purpose": "any" }
   ],
   "share_target": {
     "action": "/share-target",