Fix portrait orientation and reduce gesture sensitivity

- Rotate texture coordinates 90° for portrait mode display
  (camera sensors are landscape-oriented by default)
- Add sensitivity dampening constants for all gesture types:
  - Position drag: 0.3x
  - Rotation: 0.4x
  - Size pinch: 0.5x
  - Zoom pinch: 0.6x
- Track accumulated drag for smoother position changes

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

app/src/main/java/no/naiv/tiltshift/effect/TiltShiftRenderer.kt

@@ -44,12 +44,13 @@ class TiltShiftRenderer(
          1f,  1f   // Top right
     )
 
-    // Texture coordinates (flip Y for camera)
+    // Texture coordinates rotated 90° for portrait mode
+    // (Camera sensors are landscape-oriented, we rotate to portrait)
     private val texCoords = floatArrayOf(
-        0f, 1f,  // Bottom left
-        1f, 1f,  // Bottom right
-        0f, 0f,  // Top left
-        1f, 0f   // Top right
+        1f, 1f,  // Bottom left of screen  -> bottom right of texture
+        1f, 0f,  // Bottom right of screen -> top right of texture
+        0f, 1f,  // Top left of screen     -> bottom left of texture
+        0f, 0f   // Top right of screen    -> top left of texture
     )
 
     override fun onSurfaceCreated(gl: GL10?, config: EGLConfig?) {