fix(sticky): fixed-size creation, shared presets module, live resize sync

Fixes three review findings:

1. Sticky creation no longer zoom-adapts — always creates at M preset
   (28px/260w) in world space. Consistent at any zoom level.

2. Preset definitions extracted to stickyPresets.ts (shared domain module).
   TextFormatToolbar and tools.ts both import from there — no more
   canvas→component dependency inversion.

3. TextEditor.onLiveResize callback syncs spatial index and transform
   box as sticky background grows during typing.

frontend/src/canvas/TextEditor.ts

@@ -19,6 +19,7 @@ export class TextEditor {
   private _viewport: Viewport | null = null;
   private _container: HTMLElement | null = null;
   private _onChange: (() => void) | null = null;
+  private _onLiveResize: ((item: SceneItem) => void) | null = null;
   private _originalText: string = '';
 
   /** True when a textarea is open. */
@@ -42,6 +43,7 @@ export class TextEditor {
     viewport: Viewport,
     container: HTMLElement,
     onChange: () => void,
+    onLiveResize?: (item: SceneItem) => void,
   ): void {
     // Accept text and sticky items
     if (item.type !== 'text' && item.type !== 'sticky') return;
@@ -53,6 +55,7 @@ export class TextEditor {
     this._viewport = viewport;
     this._container = container;
     this._onChange = onChange;
+    this._onLiveResize = onLiveResize || null;
 
     const zoom = viewport.scale.x;
 
@@ -186,6 +189,7 @@ export class TextEditor {
         data.text = ta.value;
         item.displayObject.updateFromData(data);
         data.h = item.displayObject.computedHeight;
+        this._onLiveResize?.(item);
       }
     };
 
@@ -221,6 +225,7 @@ export class TextEditor {
     this._viewport = null;
     this._container = null;
     this._onChange = null;
+    this._onLiveResize = null;
     this._originalText = '';
 
     if (save) {

frontend/src/canvas/stickyPresets.ts

@@ -0,0 +1,38 @@
+/**
+ * stickyPresets — sticky note size presets (shared domain module).
+ *
+ * Defines the S/M/L/XL/XXL presets for sticky text size and card width.
+ * Used by both canvas logic (tools, SceneManager) and UI (TextFormatToolbar).
+ * No React dependencies.
+ */
+
+export type StickyTextSize = 'S' | 'M' | 'L' | 'XL' | 'XXL';
+
+export const STICKY_SIZES: StickyTextSize[] = ['S', 'M', 'L', 'XL', 'XXL'];
+
+export const STICKY_FONT_MAP: Record<StickyTextSize, number> = {
+  S: 20, M: 28, L: 36, XL: 48, XXL: 60,
+};
+
+export const STICKY_WIDTH_MAP: Record<StickyTextSize, number> = {
+  S: 200, M: 260, L: 320, XL: 400, XXL: 480,
+};
+
+/** Default preset for new sticky creation. */
+export const DEFAULT_STICKY_PRESET: StickyTextSize = 'M';
+
+/** Map a fontSize to the nearest preset label. */
+export function nearestStickySize(fontSize: number): StickyTextSize {
+  let best: StickyTextSize = 'M';
+  let bestDist = Infinity;
+  for (const size of STICKY_SIZES) {
+    const dist = Math.abs(fontSize - STICKY_FONT_MAP[size]);
+    if (dist < bestDist) { bestDist = dist; best = size; }
+  }
+  return best;
+}
+
+/** Get the card width for a given fontSize (snaps to nearest preset). */
+export function getStickyWidthForSize(fontSize: number): number {
+  return STICKY_WIDTH_MAP[nearestStickySize(fontSize)];
+}

frontend/src/canvas/tools.ts

@@ -14,7 +14,7 @@ import { DrawingSprite } from './sprites/DrawingSprite';
 import type { DrawingObject } from './scene-format';
 import { TextEditor } from './TextEditor';
 import { clampTextFontSize } from './textLimits';
-import { snapToStickyPreset } from '../components/TextFormatToolbar';
+import { DEFAULT_STICKY_PRESET, STICKY_FONT_MAP, STICKY_WIDTH_MAP } from './stickyPresets';
 
 export enum ToolType {
   SELECT = 'SELECT',
@@ -37,9 +37,6 @@ const defaultOptions: ToolOptions = {
 
 // Creation defaults — zoom-aware via screenToWorld()
 const DEFAULT_TEXT_SCREEN_FONT = 24;
-const DEFAULT_STICKY_SCREEN_FONT = 28;
-const DEFAULT_STICKY_SCREEN_WIDTH = 220;
-const DEFAULT_STICKY_SCREEN_HEIGHT = 66;
 
 type CleanupFn = (() => void) | null;
 
@@ -327,17 +324,15 @@ export function activateTool(
         const rect = container.getBoundingClientRect();
         const world = viewport.toWorld(e.clientX - rect.left, e.clientY - rect.top);
 
-        const zoom = viewport.scale.x;
-        const preset = snapToStickyPreset(screenToWorld(DEFAULT_STICKY_SCREEN_FONT, zoom, 16, 72));
-        const cardW = preset.width;
-        const cardH = screenToWorld(DEFAULT_STICKY_SCREEN_HEIGHT, zoom, 40, 200);
+        const cardW = STICKY_WIDTH_MAP[DEFAULT_STICKY_PRESET];
+        const cardH = 60; // auto-computed by StickySprite
         const stickyData = {
           id: crypto.randomUUID(),
           type: 'sticky' as const,
           x: world.x - cardW / 2,
           y: world.y - cardH / 2,
           w: cardW,
-          h: cardH,  // will be auto-computed by StickySprite
+          h: cardH,
           sx: 1,
           sy: 1,
           angle: 0,
@@ -347,7 +342,7 @@ export function activateTool(
           name: '',
           visible: true,
           text: '',
-          fontSize: preset.fontSize,
+          fontSize: STICKY_FONT_MAP[DEFAULT_STICKY_PRESET],
           fontFamily: 'Inter, system-ui, sans-serif',
           fill: '#ffd43b',     // default yellow
           textColor: '#1a1a1a',