feat(dashboard): add hide/show toggle for dashboard plugins in sidebar

- New config key: dashboard.hidden_plugins (list of plugin names)
- GET /api/dashboard/plugins now filters out hidden plugins from sidebar
- POST /api/dashboard/plugins/{name}/visibility toggles visibility
- Hub response includes user_hidden boolean per plugin row
- Eye/EyeOff toggle on plugin cards with dashboard manifests
- i18n: 'Show in sidebar' / 'Hide from sidebar' (en/zh)

web/src/i18n/en.ts

@@ -295,6 +295,8 @@ export const en: Translations = {
     authRequiredHint: "Run this command to authenticate:",
     updateGit: "Git pull",
     versionBadge: "Version",
+    showInSidebar: "Show in sidebar",
+    hideFromSidebar: "Hide from sidebar",
   },
 
   skills: {