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

server/src/dev-watch-ignore.ts

@@ -28,6 +28,9 @@ export function resolveServerDevWatchIgnorePaths(serverRoot: string): string[] {
     "../ui/node_modules/.vite-temp",
     "../ui/.vite",
     "../ui/dist",
+    // npm install during reinstall would trigger a restart mid-request
+    // if tsx watch sees the new files. Exclude the managed plugins dir.
+    process.env.HOME + "/.paperclip/adapter-plugins",
   ]) {
     addIgnorePath(ignorePaths, path.resolve(serverRoot, relativePath));
   }