feat: add 5s timeout and warning log for station name search (refs #141)

Add 5000ms timeout to Places Text Search API call in searchStationByName.
Timeout errors log a warning instead of error and return null gracefully.
Add timeout test case to station-matching unit tests.

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

backend/src/features/stations/external/google-maps/google-maps.client.ts

@@ -128,6 +128,7 @@ export class GoogleMapsClient {
             type: 'gas_station',
             key: this.apiKey,
           },
+          timeout: 5000,
         }
       );
 
@@ -145,8 +146,12 @@ export class GoogleMapsClient {
 
       await cacheService.set(cacheKey, station, this.cacheTTL);
       return station;
-    } catch (error) {
-      logger.error('Station name search failed', { error, merchantName });
+    } catch (error: any) {
+      if (error.code === 'ECONNABORTED' || error.message?.includes('timeout')) {
+        logger.warn('Station name search timed out', { merchantName, timeoutMs: 5000 });
+      } else {
+        logger.error('Station name search failed', { error, merchantName });
+      }
       return null;
     }
   }