Fix front camera rotation mirroring in shader

Add uIsFrontCamera uniform to shader and adjust coordinate
transformations for front camera's mirrored texture coordinates:
- Position transform: (1-posY, 1-posX) instead of (posY, 1-posX)
- Angle transform: -angle - 90° instead of +angle + 90°

Applied to linearFocusDistance, radialFocusDistance, and blur
direction calculations in sampleBlurred.

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

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

@@ -126,7 +126,7 @@ class TiltShiftRenderer(
         GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT)
 
         // Use shader and set parameters
-        shader.use(cameraTextureId, blurParameters, surfaceWidth, surfaceHeight)
+        shader.use(cameraTextureId, blurParameters, surfaceWidth, surfaceHeight, isFrontCamera)
 
         // Set vertex positions
         GLES20.glEnableVertexAttribArray(shader.aPositionLocation)