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/adapters/index.ts

@@ -1,4 +1,11 @@
-export { getUIAdapter, listUIAdapters } from "./registry";
+export {
+  getUIAdapter,
+  listUIAdapters,
+  findUIAdapter,
+  registerUIAdapter,
+  unregisterUIAdapter,
+  syncExternalAdapters,
+} from "./registry";
 export { buildTranscript } from "./transcript";
 export type {
   TranscriptEntry,