knowledge: include library_id in photo_links response

The PhotoLinkDetail in /knowledge/entities/{id} was dropping the
library_id field, leaving consumers no way to construct a
content-routed thumbnail URL. Apollo's curation screen was falling
through to library=0 (the FastAPI default) and getting 400s.

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

src/knowledge.rs

@@ -98,6 +98,7 @@ pub struct FactDetail {
 
 #[derive(Serialize)]
 pub struct PhotoLinkDetail {
+    pub library_id: i32,
     pub file_path: String,
     pub role: String,
 }
@@ -105,6 +106,7 @@ pub struct PhotoLinkDetail {
 impl From<EntityPhotoLink> for PhotoLinkDetail {
     fn from(l: EntityPhotoLink) -> Self {
         PhotoLinkDetail {
+            library_id: l.library_id,
             file_path: l.file_path,
             role: l.role,
         }