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/utils/exportEngine.ts

@@ -208,7 +208,7 @@ export async function processAndExportPhoto(
           FilterMode.Linear,
           MipmapMode.None
         );
-        toneShader = toneEffect.makeShaderWithChildren([tone.dr, tone.hl, tone.sh], [imageShader]);
+        toneShader = toneEffect.makeShaderWithChildren([tone.dr, tone.hl, tone.sh, tone.vib], [imageShader]);
         if (toneShader) {
           paint.setShader(toneShader);
         } else {
@@ -371,6 +371,30 @@ export async function processAndExportPhoto(
       }
     }
 
+    // 6b. Vignetting: darken the four corners of the PHOTO. Radial gradient
+    // (clear through the mid-frame, black at the corners) whose radius is the
+    // photo diagonal/2, so the falloff stays circular on any aspect. Runs
+    // before the frame step, so on a polaroid/wall export the darkening lands
+    // on the picture inside the opening, never on the mat.
+    // ponytail: one amount knob (the Fuji-style VIGNETTING control); split into
+    // amount + radius/midpoint only if users ask to move the falloff.
+    if ((adjustments.vignette ?? 0) > 0) {
+      const v = Math.min(10, adjustments.vignette ?? 0) / 10;
+      const vignetteShader = Skia.Shader.MakeRadialGradient(
+        Skia.Point(width / 2, height / 2),
+        Math.hypot(width, height) / 2,
+        [Skia.Color('rgba(0,0,0,0)'), Skia.Color('rgba(0,0,0,0)'), Skia.Color('rgba(0,0,0,1)')],
+        [0, 0.45, 1],
+        TileMode.Clamp
+      );
+      if (vignetteShader) {
+        const vignettePaint = Skia.Paint();
+        vignettePaint.setShader(vignetteShader);
+        vignettePaint.setAlphaf(0.9 * v);
+        canvas.drawRect(Skia.XYWHRect(0, 0, width, height), vignettePaint);
+      }
+    }
+
     // 7. Frame. RETRO POLAROID is not a border drawn on the photo: the whole
     // processed picture is composited, uncropped, into the window of a bigger
     // off-white card (real print proportions, see frameUtils) — the export IS