feat(collections): Add library-aware filtering to collection detail pages

- Add library_id parameter to BuildSections and getViewAllURL functions
- Update dashboard handler to pass libraryID when building sections
- Add library_id query param support to collection detail page handler
- When library_id is provided, filter collection items by that library
- When no library_id, show all books (backward compatible)
- Reuses GetCollectionItemsForDashboard query for filtered results
- Preserves context when navigating from dashboard to collection detail

internal/handlers/dashboard.go

@@ -61,7 +61,7 @@ func (h *DashboardHandler) GetSections(c echo.Context) error {
 		return c.JSON(http.StatusInternalServerError, map[string]string{"error": "Failed to load dashboard sections"})
 	}
 
-	sectionData := BuildSections(sections)
+	sectionData := BuildSections(sections, libraryID)
 
 	return c.JSON(http.StatusOK, map[string]interface{}{"sections": sectionData})
 }
@@ -154,7 +154,7 @@ func (h *DashboardHandler) RestoreSystemCollection(c echo.Context) error {
 	return c.JSON(http.StatusOK, map[string]string{"message": "System collection restored to defaults"})
 }
 
-func BuildSections(sections []services.DashboardSection) []SectionData {
+func BuildSections(sections []services.DashboardSection, currentLibraryID string) []SectionData {
 	var result []SectionData
 
 	for _, ds := range sections {
@@ -177,7 +177,7 @@ func BuildSections(sections []services.DashboardSection) []SectionData {
 			Description:  ds.Description,
 			Icon:         ds.Icon,
 			Items:        bookCards,
-			ViewAllURL:   getViewAllURL(ds.CollectionID.String()),
+			ViewAllURL:   getViewAllURL(ds.CollectionID.String(), currentLibraryID),
 			Priority:     ds.Priority,
 		})
 	}
@@ -185,8 +185,11 @@ func BuildSections(sections []services.DashboardSection) []SectionData {
 	return result
 }
 
-func getViewAllURL(collectionID string) string {
+func getViewAllURL(collectionID string, libraryID string) string {
 	if collectionID != "" {
+		if libraryID != "" {
+			return "/collections/" + collectionID + "?library_id=" + libraryID
+		}
 		return "/collections/" + collectionID
 	}
 	return ""

internal/router/frontend.go

@@ -191,8 +191,8 @@ func registerFrontendRoutes(cfg *Config) {
 			}
 		}
 
-		sectionData := handlers.BuildSections(visibleSections)
-		allSectionsData := handlers.BuildSections(allSections)
+		sectionData := handlers.BuildSections(visibleSections, libraryID)
+		allSectionsData := handlers.BuildSections(allSections, libraryID)
 
 		var buf bytes.Buffer
 		err = templates.Dashboard(user, sectionData, allSectionsData, libData, libraryID, prefs.HiddenCollections, limit, errorMsg).Render(c.Request().Context(), &buf)
@@ -358,7 +358,48 @@ func registerFrontendRoutes(cfg *Config) {
 				}
 			}
 		} else {
-			// User collection - fetch collection items
+			// User collection - check if library_id filter is present
+			libraryID := c.QueryParam("library_id")
+
+			if libraryID != "" {
+				// Filter by library - reuse dashboard query
+				libUUID, err := uuid.Parse(libraryID)
+				if err != nil {
+					return renderErrorPage(c, "Invalid library ID", "invalid_library_id")
+				}
+
+				// Use GetCollectionItemsForDashboard for library-filtered results
+				collItems, err := cfg.Queries.GetCollectionItemsForDashboard(c.Request().Context(),
+					database.GetCollectionItemsForDashboardParams{
+						CollectionID: pgtype.UUID{Bytes: collUUID, Valid: true},
+						LibraryID:    pgtype.UUID{Bytes: libUUID, Valid: true},
+						Limit:        1000,
+					})
+				if err != nil {
+					books = []handlers.BookInfo{}
+				} else {
+					// Convert to BookInfo format (non-excluded only)
+					var validItems []database.GetCollectionItemsForDashboardRow
+					for _, item := range collItems {
+						if !item.Excluded.Valid || !item.Excluded.Bool {
+							validItems = append(validItems, item)
+						}
+					}
+
+					bookCards := make([]handlers.BookInfo, len(validItems))
+					for i, item := range validItems {
+						itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
+						bookCards[i] = handlers.BookInfo{
+							MediaItemID:    itemUUID.String(),
+							Title:          item.Title,
+							Author:         getText(item.Author),
+							CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
+						}
+					}
+					books = bookCards
+				}
+			} else {
+				// No library filter - show all books in collection
 				collItems, err := cfg.Queries.GetCollectionItems(c.Request().Context(), pgtype.UUID{Bytes: collUUID, Valid: true})
 				if err != nil {
 					books = []handlers.BookInfo{}
@@ -377,6 +418,7 @@ func registerFrontendRoutes(cfg *Config) {
 				}
 				books = bookCards
 			}
+		}
 		// Build collection data
 		colData := templates.CollectionData{
 			ID:          collectionID,