feat(dashboard): add Plugins page with enable/disable, auth status, install/remove

- New PluginsPage.tsx: full plugin management UI (list, enable/disable,
  install from git, remove, git pull updates, provider picker)
- Backend: dashboard_set_agent_plugin_enabled now also toggles the
  plugin's toolset in platform_toolsets so enabling actually makes
  tools visible in agent sessions
- Backend: /api/dashboard/plugins/hub returns auth_required + auth_command
  per plugin (checks tool registry check_fn)
- Frontend: auth_required shown as Badge + CommandBlock with copy-able
  auth command
- Fix: Select overflow in providers card (min-w-0 grid cells, removed
  truncate/overflow-hidden that clipped dropdown)
- Refactor: _install_plugin_core extracted for non-interactive reuse,
  PluginOperationError for structured error handling
- i18n: en/zh/types updated with all new plugin page strings

web/src/lib/api.ts

@@ -259,6 +259,46 @@ export const api = {
   rescanPlugins: () =>
     fetchJSON<{ ok: boolean; count: number }>("/api/dashboard/plugins/rescan"),
 
+  getPluginsHub: () => fetchJSON<PluginsHubResponse>("/api/dashboard/plugins/hub"),
+
+  installAgentPlugin: (body: AgentPluginInstallRequest) =>
+    fetchJSON<AgentPluginInstallResponse>("/api/dashboard/agent-plugins/install", {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ ...body }),
+    }),
+
+  enableAgentPlugin: (name: string) =>
+    fetchJSON<{ ok: boolean; name: string; unchanged?: boolean }>(
+      `/api/dashboard/agent-plugins/${encodeURIComponent(name)}/enable`,
+      { method: "POST" },
+    ),
+
+  disableAgentPlugin: (name: string) =>
+    fetchJSON<{ ok: boolean; name: string; unchanged?: boolean }>(
+      `/api/dashboard/agent-plugins/${encodeURIComponent(name)}/disable`,
+      { method: "POST" },
+    ),
+
+  updateAgentPlugin: (name: string) =>
+    fetchJSON<AgentPluginUpdateResponse>(
+      `/api/dashboard/agent-plugins/${encodeURIComponent(name)}/update`,
+      { method: "POST" },
+    ),
+
+  removeAgentPlugin: (name: string) =>
+    fetchJSON<{ ok: boolean; name: string }>(
+      `/api/dashboard/agent-plugins/${encodeURIComponent(name)}`,
+      { method: "DELETE" },
+    ),
+
+  savePluginProviders: (body: PluginProvidersPutRequest) =>
+    fetchJSON<{ ok: boolean }>("/api/dashboard/plugin-providers", {
+      method: "PUT",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify(body),
+    }),
+
   // Dashboard themes
   getThemes: () =>
     fetchJSON<DashboardThemesResponse>("/api/dashboard/themes"),
@@ -668,8 +708,66 @@ export interface PluginManifestResponse {
     override?: string;
     hidden?: boolean;
   };
+  slots?: string[];
   entry: string;
   css?: string | null;
   has_api: boolean;
   source: string;
 }
+
+export interface HubAgentPluginRow {
+  name: string;
+  version: string;
+  description: string;
+  source: string;
+  runtime_status: "disabled" | "enabled" | "inactive";
+  has_dashboard_manifest: boolean;
+  dashboard_manifest: PluginManifestResponse | null;
+  path: string;
+  can_remove: boolean;
+  can_update_git: boolean;
+  auth_required: boolean;
+  auth_command: string;
+}
+
+export interface PluginsHubProviders {
+  memory_provider: string;
+  memory_options: Array<{ name: string; description: string }>;
+  context_engine: string;
+  context_options: Array<{ name: string; description: string }>;
+}
+
+export interface PluginsHubResponse {
+  plugins: HubAgentPluginRow[];
+  orphan_dashboard_plugins: PluginManifestResponse[];
+  providers: PluginsHubProviders;
+}
+
+export interface AgentPluginInstallRequest {
+  identifier: string;
+  force?: boolean;
+  enable?: boolean;
+}
+
+export interface AgentPluginInstallResponse {
+  ok: boolean;
+  plugin_name?: string;
+  warnings?: string[];
+  missing_env?: string[];
+  after_install_path?: string | null;
+  enabled?: boolean;
+  error?: string;
+}
+
+export interface AgentPluginUpdateResponse {
+  ok: boolean;
+  name?: string;
+  output?: string;
+  unchanged?: boolean;
+  error?: string;
+}
+
+export interface PluginProvidersPutRequest {
+  memory_provider?: string;
+  context_engine?: string;
+}