Mobile: voice and video calls (MatrixRTC with LiveKit)

Calls the way the web client and Element Call do them, with the same
events, so the three can share a call. The famedly SDK's own group calls
use com.famedly.call.member events, which the others don't read, so this
is written against the matrix-js-sdk wire format instead (lib/matrix/
calls.dart):

- Membership: org.matrix.msc3401.call.member state, key
  _@user:server_DEVICE_m.call, with the legacy session fields the js-sdk
  sends (application m.call, call_id "", membershipID, expires,
  focus_active, foci_preferred). An empty delayed copy (MSC4140) is
  scheduled first and pushed back every 5 s; leaving sends the empty
  state and cancels it.
- Media: a LiveKit token from the JWT service (the call's, else the
  homeserver's rtc/transports or .well-known rtc_foci) for an OpenID
  token; livekit_client connects.
- Encrypted rooms: a random 16-byte key per device, sent to every other
  device in the call over encrypted to-device
  io.element.call.encryption_keys, keys from others applied per LiveKit
  identity (@user:server:DEVICE); per-participant keys, no ratcheting,
  HKDF, like the web client's livekit-client.
- Ringing: a call started in a room of two sends a ring notification
  (MSC4075); the other side gets an incoming-call card and an insistent
  ringtone notification (full screen on a locked phone), declines with
  MSC4310 or answers by joining. The caller gives up after a minute or on
  a decline.
- UI: voice and video buttons in the room header, a call screen (the
  other person large and you in the corner, or a grid; mute, camera, flip,
  leave), a Join banner and a room-list marker for calls going on.

Not tested end to end yet: it needs a LiveKit SFU and JWT service.

README: replies, reactions, threads, spaces, QR verification, sliding
sync and calls.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mobile/android/app/src/main/AndroidManifest.xml

@@ -3,6 +3,15 @@
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
     <uses-permission android:name="android.permission.VIBRATE" />
+    <!-- Calls: the microphone, the camera (above), audio routing and
+         Bluetooth headsets. -->
+    <uses-permission android:name="android.permission.RECORD_AUDIO" />
+    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS" />
+    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <uses-permission android:name="android.permission.WAKE_LOCK" />
+    <!-- An incoming call shows full screen on a locked phone. -->
+    <uses-permission android:name="android.permission.USE_FULL_SCREEN_INTENT" />
     <!-- Scanning a QR code to verify a session or a person. -->
     <uses-permission android:name="android.permission.CAMERA" />
     <uses-feature android:name="android.hardware.camera" android:required="false" />
@@ -18,6 +27,8 @@
             android:name=".MainActivity"
             android:exported="true"
             android:launchMode="singleTop"
+            android:showWhenLocked="true"
+            android:turnScreenOn="true"
             android:taskAffinity=""
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"