Fix concurrency, lifecycle, performance, and config issues from audit

Concurrency & bitmap lifecycle:
- Defer bitmap recycling by one cycle so Compose finishes drawing before
  native memory is freed (preview bitmaps, thumbnails)
- Make galleryPreviewSource @Volatile for cross-thread visibility
- Join preview job before recycling source bitmap in cancelGalleryPreview()
  to prevent use-after-free during CPU blur loop
- Add @Volatile to TiltShiftRenderer.currentTexCoords (UI/GL thread race)
- Fix error dismiss race with cancellable Job tracking

Lifecycle & resource management:
- Release GL resources via glSurfaceView.queueEvent (must run on GL thread)
- Pause GLSurfaceView when entering gallery preview mode
- Shut down captureExecutor in CameraManager.release() (thread leak)
- Use WeakReference for lifecycleOwnerRef to avoid Activity GC delay
- Fix thumbnail bitmap leak on coroutine cancellation (add to finally)
- Guarantee imageProxy.close() in finally block

Performance:
- Compute gradient mask at 1/4 resolution with bilinear upscale (~93%
  less per-pixel trig work, ~75% less mask memory)
- Precompute cos/sin on CPU, pass as uCosAngle/uSinAngle uniforms
  (eliminates per-fragment transcendental calls in GLSL)
- Unroll 9-tap Gaussian blur kernel (avoids integer-branched weight
  lookup that de-optimizes on mobile GPUs)
- Add 80ms debounce to preview recomputation during slider drags

Silent failure fixes:
- Check bitmap.compress() return value; report error on failure
- Log all loadBitmapFromUri null paths (stream, dimensions, decode)
- Surface preview computation errors and ActivityNotFoundException to user
- Return boolean from writeExifToUri, log at ERROR level
- Wrap gallery preview downscale in try-catch (OOM protection)

Config:
- Add ACCESS_MEDIA_LOCATION permission (GPS EXIF on Android 10+)
- Accept coarse-only location grant for geotags
- Remove dead adjustResize (no effect with edge-to-edge)
- Set windowBackground to black (eliminates white flash on cold start)
- Add values-night theme for dark mode
- Remove overly broad ProGuard keeps (CameraX/GMS ship consumer rules)

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

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

@@ -18,7 +18,9 @@ import androidx.lifecycle.LifecycleOwner
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
+import java.lang.ref.WeakReference
 import java.util.concurrent.Executor
+import java.util.concurrent.ExecutorService
 import java.util.concurrent.Executors
 
 /**
@@ -58,11 +60,12 @@ class CameraManager(private val context: Context) {
     val isFrontCamera: StateFlow<Boolean> = _isFrontCamera.asStateFlow()
 
     /** Background executor for image capture callbacks to avoid blocking the main thread. */
-    private val captureExecutor: Executor = Executors.newSingleThreadExecutor()
+    private val captureExecutor: ExecutorService = Executors.newSingleThreadExecutor()
 
     private var surfaceTextureProvider: (() -> SurfaceTexture?)? = null
     private var surfaceSize: Size = Size(1920, 1080)
-    private var lifecycleOwnerRef: LifecycleOwner? = null
+    /** Weak reference to avoid preventing Activity GC across config changes. */
+    private var lifecycleOwnerRef: WeakReference<LifecycleOwner>? = null
 
     /**
      * Starts the camera with the given lifecycle owner.
@@ -73,7 +76,7 @@ class CameraManager(private val context: Context) {
         surfaceTextureProvider: () -> SurfaceTexture?
     ) {
         this.surfaceTextureProvider = surfaceTextureProvider
-        this.lifecycleOwnerRef = lifecycleOwner
+        this.lifecycleOwnerRef = WeakReference(lifecycleOwner)
 
         val cameraProviderFuture = ProcessCameraProvider.getInstance(context)
         cameraProviderFuture.addListener({
@@ -89,7 +92,10 @@ class CameraManager(private val context: Context) {
     }
 
     private fun bindCameraUseCases(lifecycleOwner: LifecycleOwner) {
-        val provider = cameraProvider ?: return
+        val provider = cameraProvider ?: run {
+            Log.w(TAG, "bindCameraUseCases called before camera provider initialized")
+            return
+        }
 
         // Unbind all use cases before rebinding
         provider.unbindAll()
@@ -164,12 +170,24 @@ class CameraManager(private val context: Context) {
     }
 
     /**
-     * Sets the zoom ratio.
+     * Sets the zoom ratio. Updates UI state only after the camera confirms the change.
      */
     fun setZoom(ratio: Float) {
         val clamped = ratio.coerceIn(_minZoomRatio.value, _maxZoomRatio.value)
-        camera?.cameraControl?.setZoomRatio(clamped)
-        _zoomRatio.value = clamped
+        val future = camera?.cameraControl?.setZoomRatio(clamped)
+        if (future != null) {
+            future.addListener({
+                try {
+                    future.get()
+                    _zoomRatio.value = clamped
+                } catch (e: Exception) {
+                    Log.w(TAG, "Zoom operation failed", e)
+                }
+            }, ContextCompat.getMainExecutor(context))
+        } else {
+            // Optimistic update when camera not available (e.g. during init)
+            _zoomRatio.value = clamped
+        }
     }
 
     /**
@@ -185,7 +203,7 @@ class CameraManager(private val context: Context) {
     fun switchCamera() {
         _isFrontCamera.value = !_isFrontCamera.value
         _zoomRatio.value = 1.0f  // Reset zoom when switching
-        lifecycleOwnerRef?.let { bindCameraUseCases(it) }
+        lifecycleOwnerRef?.get()?.let { bindCameraUseCases(it) }
     }
 
     /**
@@ -207,10 +225,11 @@ class CameraManager(private val context: Context) {
     }
 
     /**
-     * Releases camera resources.
+     * Releases camera resources and shuts down the background executor.
      */
     fun release() {
         cameraProvider?.unbindAll()
+        captureExecutor.shutdown()
         camera = null
         preview = null
         imageCapture = null