fix(journey): serve local file when uploading photos with Immich sync enabled

After upload, trek_photos.provider is immediately flipped to 'immich' even
though Immich's thumbnail generation is async. streamPhoto then routed to
Immich, which returned an error for the not-yet-processed asset. Because
Cache-Control was set before the proxy attempt, the error response was cached
by the browser for 24h — breaking thumbnails until a hard refresh bypassed
the cache and Immich had finished processing.

- streamPhoto now prefers the local file_path when it exists on disk,
  regardless of provider; Immich/Synology are only used when no local
  file is available (fixes the immediate broken-thumbnail symptom)
- pipeAsset sets Cache-Control: no-store on upstream errors and uses the
  caller-supplied default only on success (prevents cache poisoning)
- streamImmichAsset no longer pre-sets Cache-Control before the proxy
- streamSynologyAsset passes the same defaultCacheControl through pipeAsset

Closes #691

server/src/services/memories/synologyService.ts

@@ -661,6 +661,6 @@ export async function streamSynologyAsset(
     if (passphrase) params.append('passphrase', passphrase);
 
     const url = _buildSynologyEndpoint(synology_credentials.data.synology_url, params.toString());
-    await pipeAsset(url, response)
+    await pipeAsset(url, response, undefined, undefined, 'public, max-age=86400')
 }