apps/ui: Add widget toolbar overlay and note delete action

[youknowriad]

Summary

• Added a shared desk widget toolbar overlay rendered in tldraw’s InFrontOfTheCanvas slot.
• Added a widget-level toolbar contract so individual widgets can supply their own controls.
• Wired the sticky note widget to expose its tone picker through the new toolbar surface.
• Added a shared trailing separator and remove button so the current widget can be deleted from the toolbar.

Testing

• npx eslint --fix on the modified TypeScript files.
• npm run typecheck.
• npm test -- apps/ui/src/ui-desks/widgets/toolbar-selection.test.ts apps/ui/src/ui-desks/user-desk/tldraw-adapter.test.ts.

[wpmobilebot]

📊 Performance Test Results

Comparing 042daa8 vs trunk

app-size

Metric	trunk	042daa8	Diff	Change
App Size (Mac)	1408.80 MB	1408.80 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	042daa8	Diff	Change
load	1464 ms	1489 ms	+25 ms	⚪ 0.0%

site-startup

Metric	trunk	042daa8	Diff	Change
siteCreation	8100 ms	8100 ms	0 ms	⚪ 0.0%
siteStartup	4921 ms	4936 ms	+15 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)