feat(adapters): external adapter plugin system with dynamic UI parser

- Plugin loader: install/reload/remove/reinstall external adapters
  from npm packages or local directories
- Plugin store persisted at ~/.paperclip/adapter-plugins.json
- Self-healing UI parser resolution with version caching
- UI: Adapter Manager page, dynamic loader, display registry
  with humanized names for unknown adapter types
- Dev watch: exclude adapter-plugins dir from tsx watcher
  to prevent mid-request server restarts during reinstall
- All consumer fallbacks use getAdapterLabel() for consistent display
- AdapterTypeDropdown uses controlled open state for proper close behavior
- Remove hermes-local from built-in UI (externalized to plugin)
- Add docs for external adapters and UI parser contract

ui/src/api/adapters.ts

@@ -0,0 +1,51 @@
+/**
+ * @fileoverview Frontend API client for external adapter management.
+ */
+
+import { api } from "./client";
+
+export interface AdapterInfo {
+  type: string;
+  label: string;
+  source: "builtin" | "external";
+  modelsCount: number;
+  loaded: boolean;
+  disabled: boolean;
+  /** Installed version (for external npm adapters) */
+  version?: string;
+  /** Package name (for external adapters) */
+  packageName?: string;
+  /** Whether the adapter was installed from a local path (vs npm). */
+  isLocalPath?: boolean;
+}
+
+export interface AdapterInstallResult {
+  type: string;
+  packageName: string;
+  version?: string;
+  installedAt: string;
+}
+
+export const adaptersApi = {
+  /** List all registered adapters (built-in + external). */
+  list: () => api.get<AdapterInfo[]>("/adapters"),
+
+  /** Install an external adapter from npm or a local path. */
+  install: (params: { packageName: string; version?: string; isLocalPath?: boolean }) =>
+    api.post<AdapterInstallResult>("/adapters/install", params),
+
+  /** Remove an external adapter by type. */
+  remove: (type: string) => api.delete<{ type: string; removed: boolean }>(`/adapters/${type}`),
+
+  /** Enable or disable an adapter (disabled adapters hidden from agent menus). */
+  setDisabled: (type: string, disabled: boolean) =>
+    api.patch<{ type: string; disabled: boolean; changed: boolean }>(`/adapters/${type}`, { disabled }),
+
+  /** Reload an external adapter (bust server + client caches). */
+  reload: (type: string) =>
+    api.post<{ type: string; version?: string; reloaded: boolean }>(`/adapters/${type}/reload`, {}),
+
+  /** Reinstall an npm-sourced adapter (pulls latest from registry, then reloads). */
+  reinstall: (type: string) =>
+    api.post<{ type: string; version?: string; reinstalled: boolean }>(`/adapters/${type}/reinstall`, {}),
+};

ui/src/api/agents.ts

@@ -32,6 +32,7 @@ export interface DetectedAdapterModel {
   model: string;
   provider: string;
   source: string;
+  candidates?: string[];
 }
 
 export interface ClaudeLoginResult {