refactor(templates): generalize SeriesDetail into reusable BrowseDetail

Replace the single-purpose SeriesDetail template with a parameterized
BrowseDetail component that accepts badge icon/label, title, page title,
back URL/label, empty state icon/message, and book list. Both series
detail and new tag detail pages use the same template with different
params, eliminating duplication.

Series detail: 📚 Series, back to /series, "All Series"
Tag detail: 🏷️ Tag, back to /bookshelf, "Bookshelf"

Deleted series_detail.templ and series_detail_templ.go.
Updated frontend.go series route to call BrowseDetail with series params.
Added /tags/detail route calling BrowseDetail with tag params.

internal/router/frontend.go

@@ -269,7 +269,71 @@ func registerFrontendRoutes(cfg *Config) {
 		}
 
 		var buf bytes.Buffer
-		err = templates.SeriesDetail(user, seriesName, bookInfoList, libraryID, errorMsg).Render(c.Request().Context(), &buf)
+		err = templates.BrowseDetail(user, "📚", "Series", seriesName, seriesName, "/series", "All Series", "📚", "This series doesn't have any books in this library yet", bookInfoList, errorMsg).Render(c.Request().Context(), &buf)
+		if err != nil {
+			return err
+		}
+		return c.HTML(http.StatusOK, buf.String())
+	})
+
+	frontendProtected.GET("/tags/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
+
+		tagName := c.QueryParam("name")
+		if tagName == "" {
+			return renderErrorPage(c, "Tag 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"
+			}
+		}
+
+		var bookInfoList []handlers.BookInfo
+
+		if libraryID != "" && errorMsg == "" {
+			libUUID, err := uuid.Parse(libraryID)
+			if err == nil {
+				books, err := cfg.Queries.GetBooksByTag(c.Request().Context(), database.GetBooksByTagParams{
+					LibraryID: uuidToPGType(libUUID),
+					Column2:   tagName,
+				})
+				if err != nil {
+					log.Printf("GetBooksByTag failed: %v", err)
+					errorMsg = "Error loading tag 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.BrowseDetail(user, "🏷️", "Tag", tagName, tagName, "/bookshelf", "Bookshelf", "🏷️", "No books found with this tag", bookInfoList, errorMsg).Render(c.Request().Context(), &buf)
 		if err != nil {
 			return err
 		}