IncomingCallActivity:
- Play default ringtone (looping) when incoming call arrives
- Vibrate in phone-call pattern (1s on, 1s off, repeat)
- Respect device ringer mode (silent/vibrate/normal)
- Stop ringtone and vibration on answer, decline, or destroy

CallNotificationHelper:
- Add canUseFullScreenIntent() to check Android 14+ permission
- Add getFullScreenIntentSettingsIntent() to open system settings
- Log warning when USE_FULL_SCREEN_INTENT is not granted

The fullScreenIntent on notifications only triggers when the device is
locked. When unlocked, Android only shows a heads-up notification.

Now the service also launches IncomingCallActivity directly via
startActivity(), ensuring the full incoming call screen always appears
regardless of lock state.

The previous approach of calling startActivity() from the :reticulum
service process was silently blocked by Android 10+ background activity
launch restrictions.

Now IncomingCallActivity is launched from ServiceReticulumProtocol's
onIncomingCall callback, which runs in the main app process where
startActivity() is permitted.

Also:
- Revert the ineffective startActivity from ReticulumServiceBinder
- Add contentIntent to notification so tapping heads-up opens the call
- Bump notification priority to PRIORITY_MAX

When the app is closed and the phone is unlocked, Android 10+ blocks
startActivity() from background services. The fullScreenIntent on
notifications only launches the Activity when the device is locked.

Solution: use SYSTEM_ALERT_WINDOW ("Display over other apps") permission,
which is one of the official exemptions for background activity starts.

Changes:
- AndroidManifest: add SYSTEM_ALERT_WINDOW permission
- ReticulumServiceBinder: launch IncomingCallActivity directly from the
  foreground service when overlay permission is granted
- ServiceReticulumProtocol: also launch from UI process callback as
  fallback when app is in foreground
- CallNotificationHelper: add canDrawOverlays() and
  getOverlayPermissionSettingsIntent() helpers

The user must grant "Display over other apps" in system settings for
the incoming call screen to appear when the app is closed and the
phone is unlocked. Without it, only a heads-up notification is shown.

KeyguardManager.requestDismissKeyguard() captures the Activity in a
native IKeyguardDismissCallback$Stub that persists as a GC root even
after onDestroy(), leaking ~232 kB.

Fix:
- Remove requestDismissKeyguard from configureWindowForIncomingCall()
  (called on every onCreate, even when user doesn't answer)
- Move it to a new dismissKeyguardIfNeeded() method called only when
  the user actually answers the call
- Only dismiss if keyguard is actually locked
- Use explicit callback that clears references on completion

The previous fix (moving requestDismissKeyguard to answerCall with a
WeakReference callback) did not work because the leak is in the
framework's own anonymous class KeyguardManager$2, which captures the
Activity in its val$activity field. This is the first parameter passed
to requestDismissKeyguard(), not our callback - so we cannot prevent
the framework from retaining the Activity reference.

Solution: remove requestDismissKeyguard() entirely from
IncomingCallActivity. The keyguard dismissal will be handled by
MainActivity when it launches for the active call screen.

Also remove unused imports (KeyguardManager, Settings).

CallBridge and CallState were moved from
com.lxmf.messenger.reticulum.call.bridge to
tech.torlando.lxst.core (as CallCoordinator) in the LXST-kt submodule.

Update all references in IncomingCallActivity accordingly.

- Loop ringtone on pre-Android P using a coroutine that restarts
  playback when it stops (isLooping is only available on API 28+)
- Remove duplicate IncomingCallActivity launch from ServiceReticulumProtocol;
  the foreground service (ReticulumServiceBinder) already handles it via
  SYSTEM_ALERT_WINDOW, and the notification fullScreenIntent covers the
  locked-screen case
- Use Compose mutableStateOf for caller info so onNewIntent properly
  triggers UI recomposition with the new caller's identity and name

Cover lifecycle (finish on missing hash, survive with valid hash),
window configuration (FLAG_KEEP_SCREEN_ON), onNewIntent handling
(updates caller info, null-safe), full lifecycle without crashes,
and call state transitions (Idle/Ended/Rejected → finish).

Uses MockK to mock CallCoordinator singleton with Incoming state
so the activity doesn't auto-finish during test setup.

- Handle CallState.Busy as a finish trigger (was silently ignored)
- Fix callerName fallback passing raw hash instead of null
- Remove unused NotificationManager import
- Remove emoji from log messages for consistency
- Extract hardcoded strings to string resources for localization
- Extract hardcoded green color to named AnswerCallGreen constant
- Add unit test for CallState.Busy transition

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

Replace controller.setup() with controller.create().start() because
setup() calls visible() which idles the Robolectric main looper. The
IncomingCallActivityScreen uses rememberInfiniteTransition for the
pulsing avatar animation, which causes an infinite Choreographer frame
loop when the looper drains, hanging the test runner indefinitely.

Also adds UnconfinedTestDispatcher as Main so that lifecycleScope
coroutines (repeatOnLifecycle + StateFlow.collect) dispatch eagerly
on the current thread rather than through the looper.

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

- Call requestDismissKeyguard() when answering from lock screen so the
  mic is accessible (keyguard blocks hardware access even with
  setShowWhenLocked)
- Suppress the slide animation when transitioning from incoming call
  screen to active call screen using FLAG_ACTIVITY_NO_ANIMATION and
  overridePendingTransition(0, 0)

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