fix: BUG-13 — server geocode returns raw coords instead of location names

Root cause: server _geocode_cached() returned None → /api/geocode
returned HTTP 204 with no body. JS frontend treated 204 as success,
r.json() on empty body threw → showed raw-coordinate fallback.

Server fixes:
- _geocode_cached() now always returns a non-empty string (coordinate
  fallback when both Nominatim and reverse_geocoder fail)
- /api/geocode always returns HTTP 200 with {label: '...'} (never 204)
- /api/geocode/batch always includes every coord key in result dict
- Nominatim call: jsonv2 + accept-language=en (aligned with Pi)
- reverse_geocoder: mode=1 (aligned with Pi)

Pi alignment:
- _geocode_cached() now checks for empty reverse_geocoder label before
  returning, falling through to coordinate string (same guard as server)

server/app.py

@@ -29,29 +29,37 @@ except ImportError:
 
 @functools.lru_cache(maxsize=512)
 def _geocode_cached(lat4, lon4):
+    """Try Nominatim first (street-level), fall back to reverse_geocoder (city),
+    then raw coordinates. Always returns a non-empty label string — never None."""
     lat = lat4 / 10000.0
     lon = lon4 / 10000.0
     try:
         import urllib.request, urllib.error, json as _json
         url = (
             f"https://nominatim.openstreetmap.org/reverse"
-            f"?lat={lat}&lon={lon}&format=json&addressdetails=1"
+            f"?lat={lat}&lon={lon}&format=jsonv2&accept-language=en"
         )
         req = urllib.request.Request(url, headers={"User-Agent": "yaris-obd-server/1.0"})
         with urllib.request.urlopen(req, timeout=4) as resp:
             data = _json.loads(resp.read())
-        addr = data.get("address", {})
-        road = addr.get("road") or addr.get("pedestrian") or addr.get("cycleway", "")
-        city = addr.get("city") or addr.get("town") or addr.get("village", "")
-        return f"{road}, {city}".strip(", ") if road or city else None
+        a = data.get("address", {})
+        road = a.get("road") or a.get("hamlet") or a.get("suburb") or ""
+        city = a.get("city") or a.get("town") or a.get("village") or a.get("municipality") or ""
+        label = ", ".join(p for p in [road, city] if p)
+        if label:
+            return label
     except Exception:
         pass
+    # Offline fallback
     if _RG_AVAILABLE:
-        results = _rg.search([(lat, lon)], verbose=False)
+        results = _rg.search([(lat, lon)], mode=1, verbose=False)
         if results:
             r = results[0]
-            return f"{r.get('name', '')}, {r.get('admin1', '')}".strip(", ")
-    return None
+            label = ", ".join(p for p in [r.get("name", ""), r.get("admin1", "")] if p)
+            if label:
+                return label
+    # Last resort — raw coordinates so the frontend never gets an empty label
+    return f"{lat:.5f}, {lon:.5f}"
 
 
 app = Flask(__name__)
@@ -611,10 +619,8 @@ def geocode():
         return jsonify(error="lat and lon required"), 400
     lat4 = int(round(lat, 4) * 10000)
     lon4 = int(round(lon, 4) * 10000)
-    name = _geocode_cached(lat4, lon4)
-    if name:
-        return jsonify(label=name)
-    return jsonify(name=None), 204
+    label = _geocode_cached(lat4, lon4)
+    return jsonify(label=label)
 
 
 @app.post("/api/geocode/batch")
@@ -636,8 +642,7 @@ def geocode_batch():
         lon4 = int(round(lon, 4) * 10000)
         key = f"{lat:.3f},{lon:.3f}"
         name = _geocode_cached(lat4, lon4)
-        if name:
-            result[key] = name
+        result[key] = name
     return jsonify(result)