feat: include per-photo library id in /photos response

Adds a parallel `photo_libraries: Vec<i32>` array alongside `photos`
in `PhotosResponse` so clients can render per-thumbnail badges.
Populated with the scoped library id at the two main return sites;
left empty for `/favorites` since favorites are library-agnostic.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/data/mod.rs

@@ -102,6 +102,12 @@ pub struct PhotosResponse {
     pub photos: Vec<String>,
     pub dirs: Vec<String>,
 
+    /// Library id for each entry in `photos`, same length and ordering.
+    /// Parallel array rather than an object per row to keep the payload
+    /// small and backwards-compatible with older clients.
+    #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    pub photo_libraries: Vec<i32>,
+
     // Pagination metadata (only present when limit is set)
     #[serde(skip_serializing_if = "Option::is_none")]
     pub total_count: Option<i64>,

src/files.rs

@@ -493,9 +493,11 @@ pub async fn list_photos<TagD: TagDao, FS: FileSystemAccess>(
                 .set_attribute(KeyValue::new("total_count", total_count.to_string()));
             span_context.span().set_status(Status::Ok);
 
+            let photo_libraries = vec![scoped_library.id; tagged_files.len()];
             HttpResponse::Ok().json(PhotosResponse {
                 photos: tagged_files,
                 dirs: vec![],
+                photo_libraries,
                 total_count: pagination_metadata.0,
                 has_more: pagination_metadata.1,
                 next_offset: pagination_metadata.2,
@@ -778,9 +780,11 @@ pub async fn list_photos<TagD: TagDao, FS: FileSystemAccess>(
                 .set_attribute(KeyValue::new("total_count", total_count.to_string()));
             span_context.span().set_status(Status::Ok);
 
+            let photo_libraries = vec![scoped_library.id; response_files.len()];
             HttpResponse::Ok().json(PhotosResponse {
                 photos: response_files,
                 dirs,
+                photo_libraries,
                 total_count: pagination_metadata.0,
                 has_more: pagination_metadata.1,
                 next_offset: pagination_metadata.2,

src/main.rs

@@ -970,9 +970,12 @@ async fn favorites(
                 .collect::<Vec<String>>();
 
             span.set_status(Status::Ok);
+            // Favorites are library-agnostic (shared by rel_path), so we
+            // intentionally leave photo_libraries empty to signal "no badge".
             HttpResponse::Ok().json(PhotosResponse {
                 photos: favorites,
                 dirs: Vec::new(),
+                photo_libraries: Vec::new(),
                 total_count: None,
                 has_more: None,
                 next_offset: None,