Add contacts/phone book UI with search integration

New components:
- ContactModal.jsx: Save/edit overlay with form fields and soft delete
- ContactList.jsx: Contacts tab with filter, create, and tap-to-navigate

Modified:
- store.js: Add contacts slice (contacts, activeTab, editingContact)
- api.js: Add contacts API functions (fetch, create, update, delete, nearby)
- config.js: Add has_contacts fallback flag
- Panel.jsx: Routes/Contacts tab bar (only when has_contacts enabled)
- PlaceDetail.jsx: Save button opens ContactModal, proximity annotation
- SearchBar.jsx: Prepend matching contacts before Photon results
- App.jsx: Render ContactModal at top level
- index.css: Modal overlay, tab bar, contact list item styles

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/config.js

@@ -29,6 +29,7 @@ const FALLBACK_CONFIG = {
     has_traffic_overlay: false,
     has_landclass: false,
     has_address_book_write: false,
+    has_contacts: false,
   },
   defaults: {
     center: [42.5736, -114.6066],