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/effect/TiltShiftShader.kt

@@ -4,6 +4,8 @@ import android.content.Context
 import android.opengl.GLES11Ext
 import android.opengl.GLES20
 import no.naiv.tiltshift.R
+import kotlin.math.cos
+import kotlin.math.sin
 import java.io.BufferedReader
 import java.io.InputStreamReader
 
@@ -33,6 +35,8 @@ class TiltShiftShader(private val context: Context) {
     private var uFalloffLocation: Int = 0
     private var uAspectRatioLocation: Int = 0
     private var uResolutionLocation: Int = 0
+    private var uCosAngleLocation: Int = 0
+    private var uSinAngleLocation: Int = 0
 
     /**
      * Compiles and links the shader program.
@@ -75,6 +79,8 @@ class TiltShiftShader(private val context: Context) {
         uFalloffLocation = GLES20.glGetUniformLocation(programId, "uFalloff")
         uAspectRatioLocation = GLES20.glGetUniformLocation(programId, "uAspectRatio")
         uResolutionLocation = GLES20.glGetUniformLocation(programId, "uResolution")
+        uCosAngleLocation = GLES20.glGetUniformLocation(programId, "uCosAngle")
+        uSinAngleLocation = GLES20.glGetUniformLocation(programId, "uSinAngle")
 
         // Clean up shaders (they're linked into program now)
         GLES20.glDeleteShader(vertexShader)
@@ -103,6 +109,16 @@ class TiltShiftShader(private val context: Context) {
         GLES20.glUniform1f(uFalloffLocation, params.falloff)
         GLES20.glUniform1f(uAspectRatioLocation, params.aspectRatio)
         GLES20.glUniform2f(uResolutionLocation, width.toFloat(), height.toFloat())
+
+        // Precompute angle trig on CPU to avoid per-fragment transcendental calls.
+        // The adjusted angle accounts for the 90deg coordinate transform.
+        val adjustedAngle = if (isFrontCamera) {
+            -params.angle - (Math.PI / 2).toFloat()
+        } else {
+            params.angle + (Math.PI / 2).toFloat()
+        }
+        GLES20.glUniform1f(uCosAngleLocation, cos(adjustedAngle))
+        GLES20.glUniform1f(uSinAngleLocation, sin(adjustedAngle))
     }
 
     /**