Add 2D focus positioning, fix rotation tracking, sync preview with effect

2D positioning:
- Add positionX parameter to BlurParameters (was only Y before)
- Update shader with uPositionX and uPositionY uniforms
- Single-finger drag now moves focus center anywhere on screen
- Update gradient mask generation for capture

Rotation tracking:
- Remove dampening from rotation gesture (1:1 tracking)
- Rotate gesture now directly tracks finger movement
- Preview effect rotates in sync with overlay

Overlay and shader sync:
- Both now use same positionX, positionY, angle parameters
- Preview blur effect matches overlay visualization

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -204,7 +204,8 @@ class ImageCaptureHandler(
         val mask = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888)
         val pixels = IntArray(width * height)
 
-        val centerY = height * params.position
+        val centerX = width * params.positionX
+        val centerY = height * params.positionY
         val focusHalfHeight = height * params.size * 0.5f
         val transitionHeight = focusHalfHeight * 0.5f
 
@@ -213,8 +214,8 @@ class ImageCaptureHandler(
 
         for (y in 0 until height) {
             for (x in 0 until width) {
-                // Rotate point around center
-                val dx = x - width / 2f
+                // Rotate point around focus center
+                val dx = x - centerX
                 val dy = y - centerY
                 val rotatedY = -dx * sinAngle + dy * cosAngle