FX vignetting, LIGHT vibrance/saturation, reticle unlock

- FX: new VIGNETTING 0-10 control (chip + slider). Darkens the four
  corners of the photo with a radial gradient whose radius is the photo
  diagonal/2, so the falloff stays circular on any aspect. Applied in
  preview (camera overlay, polaroid/wall window, plain library) and in
  exportEngine pass 6b, always on the picture, never on the mat.
- LIGHT: new VIBRANCE -10..+10 (chroma-masked saturation in the tone
  shader: vivid pixels move least). Renamed the existing saturation
  control chip from COLOR to SATURATION - same param, clearer label.
- Fix: <Shader> takes a RuntimeEffect, not a gradient SkShader; the
  preview vignette threw "Object is not a HostObject" when it got one.
  Use the declarative <RadialGradient> child on the Rect instead.
- Preview: drop the "AE/AF LOCKED - TAP TO UNLOCK" banner; the lock
  reticle is now itself the unlock touch target.

src/types/index.ts

@@ -55,6 +55,8 @@ export interface ColorAdjustments {
   dynamicRange: 'auto' | 100 | 200 | 400; // Fuji-style DR tone curve (auto/100 = no extra curve)
   sharpening: number; // 0 to 10 (output screen sharpen strength)
   hdf?: number; // 0 to 10 (Highlight Diffusion Filter: glow on the highlights only)
+  vignette?: number; // 0 to 10 (darken the four corners; 0 = off)
+  vibrance?: number; // -10 to +10 (chroma-masked saturation: vivid colours move least)
   exposureCompensation: number; // -3 to +3 EV. Camera: AE bias (hardware). Library: 2^EV matrix gain.
 }