feat: text tool UX, image crop, text format toolbar, double-click focus

- Text tool: click-to-place immediately opens inline editor, auto-switches
  back to select tool. Empty text cleanup on save.
- Crop: select image + press C (or right-click > Crop) to enter crop mode.
  8 drag handles with rule-of-thirds grid, dimmed outside area.
  Enter confirms, Escape cancels. Non-destructive (stored as normalized rect).
- Text format toolbar: appears when text items selected, with font size +/-,
  font family dropdown, and color picker with presets.
- Double-click image: zoom-to-fit (PureRef-style focus)
- Entrance animation: replaced bounce with simple fade-in (no delay before
  items become interactive)
- TextEditor: allow empty text (caller handles cleanup)

frontend/src/canvas/shortcut-definitions.ts

@@ -715,4 +715,14 @@ export const shortcuts: ShortcutDef[] = [
       ctx.toggleReviewMode?.();
     },
   },
+  {
+    id: 'crop',
+    keys: { key: 'c' },
+    category: 'image',
+    description: 'Crop image',
+    needsSelection: true,
+    handler: (ctx: ShortcutContext) => {
+      ctx.startCrop?.();
+    },
+  },
 ];