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/store.js

@@ -101,4 +101,14 @@ export const useStore = create((set, get) => ({
       localStorage.removeItem('navi-theme-override')
     }
   },
+  // ── Contacts ──
+  contacts: [],
+  contactsLoaded: false,
+  activeTab: 'routes', // 'routes' | 'contacts'
+  editingContact: null, // null=closed, {}=new, {id:N}=edit
+
+  setContacts: (c) => set({ contacts: c, contactsLoaded: true }),
+  setActiveTab: (tab) => set({ activeTab: tab }),
+  setEditingContact: (c) => set({ editingContact: c }),
+  clearEditingContact: () => set({ editingContact: null }),
 }))