feat(navi): address book with geocoding integration

- YAML-backed saved locations (config/address_book.yaml)
- Exact/partial alias matching with case-insensitive lookup
- Flask blueprint: /api/address_book/lookup, /api/address_book/list
- Geocoder short-circuits Photon when address book has exact match
- Test suite for lookup behavior

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

lib/api.py

@@ -44,6 +44,11 @@ app = Flask(__name__,
 
 app.config['MAX_CONTENT_LENGTH'] = None  # ZIM files can be multi-GB
 
+# ── Address Book Blueprint ──
+from .address_book_api import address_book_bp
+app.register_blueprint(address_book_bp)
+
+
 # ── Navigation Constants ──
 
 KNOWLEDGE_SUBNAV = [