Fix state persistence, drag tracking, and shader rotation sync

State persistence:
- Use rememberUpdatedState to always get latest params inside pointerInput
- Capture gestureStartParams at beginning of each gesture
- All adjustments now use initial values + accumulated change

Drag tracking:
- Track initialDragCentroid at drag start
- Calculate total drag offset from initial point (not frame-by-frame)
- Drag now properly moves focus center 1:1

Shader rotation sync:
- Adjust angle by -90° in shader to compensate for portrait texture rotation
- Preview blur effect now rotates in sync with overlay UI

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

app/src/main/res/raw/tiltshift_fragment.glsl

@@ -24,8 +24,10 @@ float focusDistance(vec2 uv) {
     vec2 center = vec2(uPositionX, uPositionY);
     vec2 offset = uv - center;
 
-    float cosA = cos(uAngle);
-    float sinA = sin(uAngle);
+    // Adjust angle by -90 degrees to compensate for portrait texture rotation
+    float adjustedAngle = uAngle - 1.5707963;
+    float cosA = cos(adjustedAngle);
+    float sinA = sin(adjustedAngle);
 
     // After rotation, measure perpendicular distance from center line
     float rotatedY = -offset.x * sinA + offset.y * cosA;
@@ -70,8 +72,8 @@ vec4 sampleBlurred(vec2 uv, float blur) {
     vec4 color = vec4(0.0);
     vec2 texelSize = 1.0 / uResolution;
 
-    // Blur direction perpendicular to focus line
-    float blurAngle = uAngle + 1.5707963; // +90 degrees
+    // Blur direction perpendicular to focus line (adjusted for portrait texture rotation)
+    float blurAngle = uAngle; // Already perpendicular after -90 adjustment in focusDistance
     vec2 blurDir = vec2(cos(blurAngle), sin(blurAngle));
 
     // Scale blur radius by blur amount