Edit the watermark in place, rotate the frame photo, place a custom watermark

Watermark editing no longer covers the photo: the preview letterboxes the
image inside its fit rect while the deck is open, and the idle hint is gone.

The FRAME tab can rotate a library photo 90 degrees clockwise. Rotation
swaps the pixel dimensions instead of the frame, so the polaroid/wall window
keeps its aspect and every consumer (cover crop, watermark area, export) picks
up the new orientation from width()/height() with no extra layout branch. The
rotate surface is CPU-backed on purpose - a GPU snapshot loses its pixels
before the next frame and renders the photo black.

Custom watermark text can now be dragged anywhere on the photo, double-tapped
to re-edit, and is only baked into the file once ACCEPT is pressed; the export
engine takes the same position. It also gained COLOR/SIZE/FONT chips, with the
font list read from the OS via Skia's FontMgr so any installed family can be
used.

src/types/index.ts

@@ -87,4 +87,10 @@ export interface CustomWatermark {
   text: string;
   x: number;
   y: number;
+  // Styling set by the COLOR / SIZE / FONT chips. Absent on marks saved before
+  // those controls existed — the renderers then fall back to amber, 1x and the
+  // bundled Cousine face, i.e. exactly the previous look.
+  color?: string;
+  size?: number; // multiplier on the base 3.2%-of-width text size
+  font?: string | null; // OS font family; null/absent = bundled font
 }