feat(settings): sync preferences across devices via io.lotus.settings account data (#104)

Every Lotus setting was localStorage-only, so a user on web + desktop + phone
configured theme, composer toolbar, quiet hours, call keys… three times.

- utils/settingsSync.ts (pure, 7 tests): DEVICE_LOCAL_KEYS denylist (zoom,
  media auto-load, animation pause, glassmorphism, denoise tier/model,
  bitrates, volumes, notification permission, developer tools, PTT mode,
  camera-on-join, drawer state, and the sync toggle itself), pickSyncable,
  mergeRemoteSettings (unknown keys, device-local keys and wrong-shaped
  values are skipped), buildSyncedContent, shouldApplyRemote (LWW on
  updatedAt; equal stamp = our own echo).
- hooks/useSettingsSync.ts: on start applies a newer remote snapshot or
  pushes local if it differs; debounced push on any settingsAtom write,
  skipped when the syncable subset equals the last pushed/applied snapshot
  so a remote apply never echoes back; AccountData listener for live
  updates; stamps forced monotonic per device; per-account lastSyncedAt
  marker so another user on the same device can't inherit it; failed pushes
  roll the marker back so the next change retries. Remote values are re-read
  through getSettings() so enum coercion applies.
- Settings → General → Sync: toggle (device-local), "Push now", "Clear
  synced copy". AccountDataEvent.LotusSettings registered.
- ClientNonUIFeatures: the #103 tracking-param subscriber moves out of
  PageZoomFeature into its own TrackingParamsFeature next to
  SettingsSyncFeature.
- Docs: LOTUS_FEATURES entries for #103/#104; LOTUS_TODO links the new
  Features 2026-Q4 milestone and #108.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

LOTUS_TODO.md

@@ -236,7 +236,7 @@ After Phases A–C the client spec is ~complete. What's left, flagged by **what
 
 **✅ Buildable NOW (client-only, no server/infra change):**
 
-- [ ] **Custom room tags / sections** — user-defined room categories in the sidebar via standard `u.*` room tags (beyond the built-in Favourite / Low-Priority). Mirrors the favourite/low-priority category pattern (`RoomNavItem` context-menu + `Home.tsx` categories). _Medium._ The only substantive client-only feature left.
+- [ ] **Custom room tags / sections** (Gitea **#108**, milestone _Features 2026-Q4_) — user-defined room categories in the sidebar via standard `u.*` room tags (beyond the built-in Favourite / Low-Priority). Mirrors the favourite/low-priority category pattern (`RoomNavItem` context-menu + `Home.tsx` categories). _Medium._ The only substantive client-only feature left.
 
 **🔧 Needs INFRASTRUCTURE (NOT a Synapse-flag flip — you'd have to stand it up):**
 
@@ -258,6 +258,8 @@ After Phases A–C the client spec is ~complete. What's left, flagged by **what
 
 ## 📋 Open Feature Backlog
 
+**Features 2026-Q4 milestone (Gitea):** #103 tracking-param stripping ✅ · #104 settings sync ✅ · #105 desktop keychain + idle lock (research) · #106 search operators (research) · #107 paste-as-code (research) · #108 custom room sections.
+
 ### [ ] Basic in-app audio editor / video→audio extractor (LARGE PROJECT)
 
 A minimal audio editor for soundboard clips and voice content. Scope: (1) **trim/clip** an audio file to a chosen start/end (waveform scrubber, in/out handles); (2) **upload a video file → strip and discard the video track, keep only the audio** (extract audio, then the source video is dropped — never uploaded/stored); (3) minimal edits only (trim, maybe gain/normalize, fade in/out) — not a full DAW. Likely Web Audio API (`AudioContext.decodeAudioData` → trim `AudioBuffer` → re-encode) + `MediaRecorder`/an encoder for output; video demux via a `<video>`+`MediaElementSource` capture or ffmpeg.wasm (weigh bundle cost). Feeds the soundboard uploader (`utils/soundboardClips.ts`, `SoundboardPackEditor`) and attachments. Design under TDS + native-cinny law. Big build — plan a dedicated session; evaluate ffmpeg.wasm size/CSP (wasm) before committing.