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/immichService.ts

@@ -246,8 +246,7 @@ export async function streamImmichAsset(
     ? `${creds.immich_url}/api/assets/${assetId}/thumbnail?size=thumbnail`
     : `${creds.immich_url}/api/assets/${assetId}/thumbnail?size=fullsize`;
 
-  response.set('Cache-Control', 'public, max-age=86400');
-  await pipeAsset(url, response, { 'x-api-key': creds.immich_api_key }, AbortSignal.timeout(timeout));
+  await pipeAsset(url, response, { 'x-api-key': creds.immich_api_key }, AbortSignal.timeout(timeout), 'public, max-age=86400');
 }
 
 // ── Albums ──────────────────────────────────────────────────────────────────