feat: 添加站点设置中的 favicon URL 支持，更新相关接口和页面

admin/src/lib/types.ts

@@ -412,6 +412,7 @@ export interface AdminSiteSettingsResponse {
   media_r2_public_base_url: string | null
   media_r2_access_key_id: string | null
   media_r2_secret_access_key: string | null
+  seo_favicon_url: string | null
   seo_default_og_image: string | null
   seo_default_twitter_handle: string | null
   seo_wechat_share_qr_enabled: boolean
@@ -489,6 +490,7 @@ export interface SiteSettingsPayload {
   mediaR2PublicBaseUrl?: string | null
   mediaR2AccessKeyId?: string | null
   mediaR2SecretAccessKey?: string | null
+  seoFaviconUrl?: string | null
   seoDefaultOgImage?: string | null
   seoDefaultTwitterHandle?: string | null
   seoWechatShareQrEnabled?: boolean

admin/src/pages/site-settings-page.tsx

@@ -216,6 +216,7 @@ function toPayload(form: AdminSiteSettingsResponse): SiteSettingsPayload {
     mediaR2PublicBaseUrl: form.media_r2_public_base_url,
     mediaR2AccessKeyId: form.media_r2_access_key_id,
     mediaR2SecretAccessKey: form.media_r2_secret_access_key,
+    seoFaviconUrl: form.seo_favicon_url,
     seoDefaultOgImage: form.seo_default_og_image,
     seoDefaultTwitterHandle: form.seo_default_twitter_handle,
     seoWechatShareQrEnabled: form.seo_wechat_share_qr_enabled,
@@ -915,6 +916,22 @@ export function SiteSettingsPage() {
               </CardDescription>
             </CardHeader>
             <CardContent className="grid gap-6 lg:grid-cols-2">
+              <Field label="Favicon URL" hint="浏览器标签页图标；支持外链，也支持上传 / 抓取 / 选择媒体库。">
+                <div className="space-y-3">
+                  <Input
+                    value={form.seo_favicon_url ?? ''}
+                    onChange={(event) => updateField('seo_favicon_url', event.target.value)}
+                  />
+                  <MediaUrlControls
+                    value={form.seo_favicon_url ?? ''}
+                    onChange={(seoFaviconUrl) => updateField('seo_favicon_url', seoFaviconUrl)}
+                    prefix="seo-assets/"
+                    contextLabel="站点 favicon 上传"
+                    remoteTitle={form.site_name || form.site_title || '站点 favicon'}
+                    dataTestIdPrefix="site-favicon"
+                  />
+                </div>
+              </Field>
               <Field label="默认 OG 图 URL" hint="文章未单独设置时作为分享图回退，也支持上传 / 抓取 / 选择媒体库。">
                 <div className="space-y-3">
                   <Input