feat(sdk-app): add command palette for page navigation

[jeffredodd]

Summary

• Adds a Spotlight-style command palette to the SDK dev app: ⌘K opens a floating search box that filters across every navigable page (SDK component previews + design prototypes + Home / Design Home).
• Arrow keys highlight, Enter navigates, Esc / backdrop click closes. Highlighted result auto-scrolls into view.
• Pages list is built once at module load by merging the existing componentRegistry and design categorizedRegistry — no new metadata to maintain.
• Mirrors the ShortcutHelper folder/hook layout but uses its own bare-input visual (no modal header/title/close button). Theming reuses existing CSS variables.
• Helper modal (?) now lists ⌘K — Open page search.

Demo

Search.Demo.mov

Test plan

• npm run sdk-app and press ⌘K — bare floating search box appears, input focused
• Type onboard — filtered list across Company / Contractor / Employee previews + Design contractor self-onboarding
• Arrow ↓ / ↑ moves the highlight without moving the input cursor; long lists auto-scroll the highlighted row into view
• Enter on a highlighted row navigates and closes the palette; query resets on next open
• Esc closes; backdrop click closes
• Open the sidebar's component-search input, focus it, then press ⌘K — palette still opens (mod shortcut bypasses typing-target check)
• Press ? and confirm ⌘ K — Open page search is listed in the helper modal
• npm run tsc and lint stay clean

🤖 Generated with Claude Code