Fix CameraX GL surface: render-on-demand, crop-to-fill, lifecycle

- Switch GLSurfaceView from RENDERMODE_CONTINUOUSLY to RENDERMODE_WHEN_DIRTY
  with OnFrameAvailableListener, halving GPU work
- Add crop-to-fill aspect ratio correction so camera preview is not
  stretched on displays with non-16:9 aspect ratios
- Add LifecycleEventObserver to pause/resume GLSurfaceView with Activity
  lifecycle, preventing background rendering and GL context issues

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

app/src/main/java/no/naiv/tiltshift/camera/CameraManager.kt

@@ -59,6 +59,9 @@ class CameraManager(private val context: Context) {
     private val _isFrontCamera = MutableStateFlow(false)
     val isFrontCamera: StateFlow<Boolean> = _isFrontCamera.asStateFlow()
 
+    private val _previewResolution = MutableStateFlow(Size(0, 0))
+    val previewResolution: StateFlow<Size> = _previewResolution.asStateFlow()
+
     /** Background executor for image capture callbacks to avoid blocking the main thread. */
     private val captureExecutor: ExecutorService = Executors.newSingleThreadExecutor()
 
@@ -161,6 +164,7 @@ class CameraManager(private val context: Context) {
         }
 
         surfaceSize = request.resolution
+        _previewResolution.value = surfaceSize
         surfaceTexture.setDefaultBufferSize(surfaceSize.width, surfaceSize.height)
 
         val surface = Surface(surfaceTexture)