docs: add android text-formatting parity gap

docs/backend-web-android-parity.md

@@ -23,6 +23,13 @@ Backend покрывает web-функционал почти полность
 - `DELETE /api/v1/notifications/push-token`
 - `POST /api/v1/auth/resend-verification`
 
+## 2.1) Web feature parity gaps not yet covered on Android
+
+- Text formatting in composer/render is not at web parity yet:
+  - bold / italic / underline / strikethrough
+  - spoiler / monospace / code block / links
+  - shortcut/toolbar UX similar to web composer
+
 ## 3) Practical status
 
 - Backend readiness vs Web: `high`
@@ -35,3 +42,4 @@ Backend покрывает web-функционал почти полность
 - `GET /api/v1/messages/{message_id}/thread` (UI usage)
 - notifications API + UI inbox flow
 - notifications delivery polish (channels/grouping/snooze/per-chat overrides parity with web prefs)
+- text formatting parity in chat composer/render