feat(series): add dedicated series detail page instead of bookshelf filter

Create a new /series/detail?name=X&library_id=Y SSR page that shows
all books in a specific series, replacing the broken approach of
linking to /bookshelf?series_filter=X (the bookshelf SSR handler
ignores all filter query params).

The series detail page features:
- Back link to /series browse page
- Library selector dropdown (full page navigation on change)
- Series name header with book count badge
- Book grid using the shared BookCard template
- Empty state for series with no books

Update all links to point to the new page:
- Series cards on /series browse page
- Series badge on book detail page
- JS-rendered cards in series.ts switchLibrary

Add seriesDetailPage Alpine component for the detail page's
library switcher (simple navigation, no AJAX needed).

internal/router/frontend.go

@@ -213,6 +213,89 @@ func registerFrontendRoutes(cfg *Config) {
 		return c.HTML(http.StatusOK, buf.String())
 	})
 
+	// Series detail page (books in a specific series)
+	frontendProtected.GET("/series/detail", func(c *echo.Context) error {
+		user, err := getTemplateUserWithTheme(c, cfg)
+		if err != nil {
+			return renderErrorPage(c, "Error loading user", "user_load_error")
+		}
+
+		var errorMsg string
+
+		seriesName := c.QueryParam("name")
+		if seriesName == "" {
+			return renderErrorPage(c, "Series name required", "bad_request")
+		}
+
+		libraryID := c.QueryParam("library_id")
+		userUUID, _ := uuid.Parse(user.ID)
+		if libraryID == "" {
+			libraries, err := cfg.Queries.GetUserVisibleLibraries(c.Request().Context(), uuidToPGType(userUUID))
+			if err == nil && len(libraries) > 0 {
+				libUUID, _ := uuid.FromBytes(libraries[0].ID.Bytes[0:16])
+				libraryID = libUUID.String()
+			} else {
+				errorMsg = "No libraries available"
+			}
+		}
+
+		libraries, err := cfg.Queries.GetUserVisibleLibraries(c.Request().Context(), uuidToPGType(userUUID))
+		if err != nil {
+			log.Printf("GetUserVisibleLibraries failed: %v", err)
+			libraries = []database.GetUserVisibleLibrariesRow{}
+			if errorMsg == "" {
+				errorMsg = "Error loading libraries"
+			}
+		}
+
+		libData := make([]templates.LibraryData, len(libraries))
+		for i, lib := range libraries {
+			libUUID, _ := uuid.FromBytes(lib.ID.Bytes[0:16])
+			libData[i] = templates.LibraryData{
+				ID:          libUUID.String(),
+				Name:        lib.Name,
+				Description: getText(lib.Description),
+				TypeName:    lib.TypeName,
+			}
+		}
+
+		var bookInfoList []handlers.BookInfo
+
+		if libraryID != "" && errorMsg == "" {
+			libUUID, err := uuid.Parse(libraryID)
+			if err == nil {
+				svc := services.NewSeriesService(cfg.Queries)
+				books, err := svc.GetSeriesBooks(c.Request().Context(), libUUID, seriesName)
+				if err != nil {
+					log.Printf("GetSeriesBooks failed: %v", err)
+					errorMsg = "Error loading series books"
+				} else {
+					bookInfoList = make([]handlers.BookInfo, 0, len(books))
+					for _, item := range books {
+						itemUUID, _ := uuid.FromBytes(item.ID.Bytes[0:16])
+						bookInfoList = append(bookInfoList, handlers.BookInfo{
+							MediaItemID:    itemUUID.String(),
+							Title:          item.Title,
+							Author:         textToString(item.Author),
+							CoverImagePath: utils.ResolveMediaURL(item.LibraryID, item.CoverImagePath),
+						})
+					}
+				}
+			}
+		}
+
+		if bookInfoList == nil {
+			bookInfoList = []handlers.BookInfo{}
+		}
+
+		var buf bytes.Buffer
+		err = templates.SeriesDetail(user, seriesName, bookInfoList, libData, libraryID, errorMsg).Render(c.Request().Context(), &buf)
+		if err != nil {
+			return err
+		}
+		return c.HTML(http.StatusOK, buf.String())
+	})
+
 	frontendProtected.GET("/bookshelf", func(c *echo.Context) error {
 		user, err := getTemplateUserWithTheme(c, cfg)
 		if err != nil {