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/registry.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it, beforeEach, afterEach } from "vitest";
+import type { UIAdapterModule } from "./types";
+import {
+  findUIAdapter,
+  getUIAdapter,
+  listUIAdapters,
+  registerUIAdapter,
+  unregisterUIAdapter,
+} from "./registry";
+import { processUIAdapter } from "./process";
+
+const externalUIAdapter: UIAdapterModule = {
+  type: "external_test",
+  label: "External Test",
+  parseStdoutLine: () => [],
+  ConfigFields: () => null,
+  buildAdapterConfig: () => ({}),
+};
+
+describe("ui adapter registry", () => {
+  beforeEach(() => {
+    unregisterUIAdapter("external_test");
+  });
+
+  afterEach(() => {
+    unregisterUIAdapter("external_test");
+  });
+
+  it("registers adapters for lookup and listing", () => {
+    registerUIAdapter(externalUIAdapter);
+
+    expect(findUIAdapter("external_test")).toBe(externalUIAdapter);
+    expect(getUIAdapter("external_test")).toBe(externalUIAdapter);
+    expect(listUIAdapters().some((adapter) => adapter.type === "external_test")).toBe(true);
+  });
+
+  it("falls back to the process parser for unknown types after unregistering", () => {
+    registerUIAdapter(externalUIAdapter);
+
+    unregisterUIAdapter("external_test");
+
+    expect(findUIAdapter("external_test")).toBeNull();
+    const fallback = getUIAdapter("external_test");
+    // Unknown types return a lazy-loading wrapper (for external adapters),
+    // not the process adapter directly. The type is preserved.
+    expect(fallback.type).toBe("external_test");
+    // But it uses the process parser under the hood.
+    expect(fallback.ConfigFields).toBe(processUIAdapter.ConfigFields);
+  });
+});