refactor(sticky): fixed-width card with S/M/L/XL/XXL font presets

Stickies are now fixed-width cards — no resize handles shown.
Text size controlled via 5 presets (10/14/18/24/32px).
On creation, zoom-aware screenToWorld snaps to nearest preset.
Height auto-adjusts from content. Plain text resize unchanged.

Removes: sticky width bake, live reflow drag, min width constraint.
Backward compatible — existing stickies map to nearest preset.

frontend/src/canvas/tools.ts

@@ -13,7 +13,8 @@ import type { SelectionManager } from './SelectionManager';
 import { DrawingSprite } from './sprites/DrawingSprite';
 import type { DrawingObject } from './scene-format';
 import { TextEditor } from './TextEditor';
-import { clampTextFontSize, clampStickyFontSize } from './textLimits';
+import { clampTextFontSize } from './textLimits';
+import { snapToStickyPreset } from '../components/TextFormatToolbar';
 
 export enum ToolType {
   SELECT = 'SELECT',
@@ -345,7 +346,7 @@ export function activateTool(
           name: '',
           visible: true,
           text: '',
-          fontSize: clampStickyFontSize(screenToWorld(DEFAULT_STICKY_SCREEN_FONT, zoom, 8, 96)),
+          fontSize: snapToStickyPreset(screenToWorld(DEFAULT_STICKY_SCREEN_FONT, zoom, 8, 40)),
           fontFamily: 'Inter, system-ui, sans-serif',
           fill: '#ffd43b',     // default yellow
           textColor: '#1a1a1a',