feat: fit-contain letterbox + smart queue refill

- Replace center-crop with fit-contain (no photo cropping)
- Letterbox bars filled with adjacent edge average color
- Queue fetches in batches until 50 usable assets
- Auto-refill queue on exhaustion, dedup via shown history
- Filter RAW files from asset selection

Co-authored-by: Cursor <cursoragent@cursor.com>

src/immich_client.h

@@ -26,6 +26,7 @@ public:
     void begin(const String& baseUrl, const String& apiKey);
     std::vector<AlbumInfo> fetchAlbums();
     std::vector<String> fetchAlbumAssetIds(const String& albumId);
+    std::vector<String> fetchRandomAssetIds(int count = 50);
     std::vector<String> fetchFavoriteAssetIds();
     AssetInfo fetchAssetInfo(const String& assetId);
     bool downloadAsset(const String& assetId, ImageQuality quality,
@@ -37,5 +38,7 @@ private:
 
     String buildUrl(const String& path);
     String httpGet(const String& url);
+    String httpPost(const String& url, const String& body);
+    char* httpGetPsram(const String& url, size_t* outLen);
     bool httpGetBinary(const String& url, uint8_t** outBuffer, size_t* outSize);
 };