Add interactive gallery preview before applying tilt-shift effect

Instead of immediately processing gallery images, show a preview where
users can adjust blur parameters before committing. Adds Cancel/Apply
buttons and hides camera-only controls during gallery preview mode.

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

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

@@ -189,6 +189,21 @@ class ImageCaptureHandler(
         return BitmapFactory.decodeByteArray(bytes, 0, bytes.size)
     }
 
+    /**
+     * Loads a gallery image and applies EXIF rotation, returning the bitmap for preview.
+     * The caller owns the returned bitmap and is responsible for recycling it.
+     */
+    suspend fun loadGalleryImage(imageUri: Uri): Bitmap? = withContext(Dispatchers.IO) {
+        try {
+            val bitmap = loadBitmapFromUri(imageUri)
+                ?: return@withContext null
+            applyExifRotation(imageUri, bitmap)
+        } catch (e: Exception) {
+            Log.e(TAG, "Failed to load gallery image for preview", e)
+            null
+        }
+    }
+
     /**
      * Processes an existing image from the gallery through the tilt-shift pipeline.
      * Loads the image, applies EXIF rotation, processes the effect, and saves both versions.