feat(desktop): tray Do-Not-Disturb + Launch-on-login toggle (P6-1 web)

- useTauriDnd + manualDndAtom: the native tray "Do Not Disturb" toggle
  (lotus-dnd-changed event) OR's into the notification quiet-gate in
  ClientNonUIFeatures (both invite + message notifiers), alongside Focus Assist.
- AutostartSetting in Settings → General (desktop-only): reads/sets
  plugin:autostart via invoke. Mirrors the window-chrome setting.
- Docs: LOTUS_FEATURES desktop section (Linux parity + DND + autostart),
  LOTUS_TODO P6-1 → [~], LOTUS_BUGS verification row.

Gates: tsc/eslint/prettier clean, build OK, 661 tests. Native side committed on
cinny-desktop:main (CI-compile-pending).

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

LOTUS_TODO.md

@@ -513,7 +513,7 @@ Check back after each Synapse upgrade — re-run `/matrix/client/versions` and `
 
 Buildable follow-ups surfaced by the deep-audit wave. Web Push (N107) deliberately deferred. **macOS is out of scope for all of these — Linux is the parity target (Windows already has most native features).**
 
-### [ ] P6-1 · Desktop — cross-platform parity (Linux + Windows; NO macOS)
+### [~] P6-1 · Desktop — cross-platform parity (Linux + Windows; NO macOS) — IMPLEMENTED (2026-07); native CI-compile-pending, runtime-verify on Linux
 
 From the desktop audit. Round out the native app now that the full Rust stack compiles: