feat(navi): add netsyms tier-2 geocoding + geocode API

Add Netsyms AddressDatabase2025 (159M US+CA addresses) as tier-2
in the geocode chain: address_book → netsyms → photon.

- lib/netsyms.py: SQLite lookup module (lazy, read-only, thread-safe)
- lib/netsyms_api.py: Flask blueprints for /api/netsyms/* and /api/geocode
- lib/netsyms_test.py: 7 test cases (street, free-text, zipcode, health)
- lib/nav_tools.py: new geocode() with consistent {name,lat,lon,source,raw}
- lib/api.py: register netsyms_bp and geocode_bp

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

lib/api.py

@@ -48,6 +48,11 @@ app.config['MAX_CONTENT_LENGTH'] = None  # ZIM files can be multi-GB
 from .address_book_api import address_book_bp
 app.register_blueprint(address_book_bp)
 
+# ── Netsyms + Geocode Blueprints ──
+from .netsyms_api import netsyms_bp, geocode_bp
+app.register_blueprint(netsyms_bp)
+app.register_blueprint(geocode_bp)
+
 
 # ── Navigation Constants ──