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/index.css

@@ -469,3 +469,69 @@ body {
     opacity: 0.6;
   }
 }
+
+/* ═══ CONTACT MODAL ═══ */
+.contact-modal-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 50;
+  background: rgba(0, 0, 0, 0.5);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.contact-modal {
+  background: var(--bg-raised);
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  width: 90%;
+  max-width: 420px;
+  max-height: 85vh;
+  overflow-y: auto;
+  padding: 20px;
+  box-shadow: var(--shadow-lg);
+}
+
+/* ═══ PANEL TAB BAR ═══ */
+.navi-tab-bar {
+  display: flex;
+  gap: 4px;
+  border-bottom: 1px solid var(--border-subtle);
+}
+
+.navi-tab {
+  padding: 6px 12px;
+  font-size: var(--text-xs);
+  font-weight: 500;
+  color: var(--text-tertiary);
+  background: transparent;
+  border: none;
+  border-bottom: 2px solid transparent;
+  cursor: pointer;
+  transition: color 0.1s, border-color 0.1s;
+}
+
+.navi-tab:hover {
+  color: var(--text-secondary);
+}
+
+.navi-tab-active {
+  color: var(--accent);
+  border-bottom-color: var(--accent);
+}
+
+/* ═══ CONTACT LIST ITEMS ═══ */
+.contact-item {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 8px;
+  border-radius: 8px;
+  cursor: pointer;
+  transition: background 0.1s;
+}
+
+.contact-item:hover {
+  background: var(--bg-overlay);
+}