feat: add favicon settings to site configuration

- Add Favicon field to SiteSetting model with FaviconIsURL() helper
- Implement favicon upload and management in site settings page
- Support both external URL and local file upload for favicon
- Add favicon display in page header with automatic URL detection
- Add i18n translations for favicon settings (EN/ZH)
- Update middleware and helpers to pass favicon data to templates
- Include migration script for existing databases

Users can now customize their site's favicon from /admin/settings/site
by either providing an external URL or uploading a local image file
(recommended formats: .ico, .png, .svg, 16x16 or 32x32 pixels).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

handlers/settings.go

@@ -74,6 +74,7 @@ func SiteSettingsPage(db *gorm.DB) gin.HandlerFunc {
 		// Pre-compute derived values so the template never invokes methods on
 		// an interface{}-wrapped struct (which Go templates cannot resolve).
 		data["SiteLogoIsURL"] = s.LogoIsURL()
+		data["SiteFaviconIsURL"] = s.FaviconIsURL()
 		if msg := c.Query("saved"); msg == "1" {
 			data["Success"] = tr["settings_saved"]
 		}
@@ -101,6 +102,46 @@ func SiteSettingsSave(db *gorm.DB, storagePath string) gin.HandlerFunc {
 		s.FooterTextEn = strings.TrimSpace(c.PostForm("footer_text_en"))
 		s.UpdatedBy = userIDFromSession(c)
 
+		// Favicon upload (optional). A favicon_url form field takes precedence over an
+		// uploaded file, so admins can set either a local file or an external link.
+		if faviconURL := strings.TrimSpace(c.PostForm("favicon_url")); faviconURL != "" {
+			s.Favicon = faviconURL
+		} else if file, header, err := c.Request.FormFile("favicon"); err == nil {
+			defer file.Close()
+			check := ValidateUpload(header)
+			if !check.OK || check.Type.Category != models.CategoryImage {
+				c.Redirect(http.StatusFound, "/admin/settings/site")
+				return
+			}
+			logoDir := filepath.Join(storagePath, "logos")
+			os.MkdirAll(logoDir, 0755)
+			// Remove the previous local favicon (skip external URLs).
+			if s.Favicon != "" && !s.FaviconIsURL() {
+				os.Remove(filepath.Join(logoDir, s.Favicon))
+			}
+			ext := strings.ToLower(filepath.Ext(header.Filename))
+			savedName := fmt.Sprintf("favicon%s", ext)
+			dst, err := os.Create(filepath.Join(logoDir, savedName))
+			if err != nil {
+				c.Redirect(http.StatusFound, "/admin/settings/site")
+				return
+			}
+			defer dst.Close()
+			if _, err := io.Copy(dst, file); err != nil {
+				c.Redirect(http.StatusFound, "/admin/settings/site")
+				return
+			}
+			s.Favicon = savedName
+		}
+
+		// Remove favicon entirely if requested.
+		if c.PostForm("favicon_clear") == "1" {
+			if s.Favicon != "" && !s.FaviconIsURL() {
+				os.Remove(filepath.Join(storagePath, "logos", s.Favicon))
+			}
+			s.Favicon = ""
+		}
+
 		// Logo upload (optional). A logo_url form field takes precedence over an
 		// uploaded file, so admins can set either a local file or an external link.
 		if logoURL := strings.TrimSpace(c.PostForm("logo_url")); logoURL != "" {