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/metadata.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { isEnabledAdapterType, listAdapterOptions } from "./metadata";
+import type { UIAdapterModule } from "./types";
+
+const externalAdapter: UIAdapterModule = {
+  type: "external_test",
+  label: "External Test",
+  parseStdoutLine: () => [],
+  ConfigFields: () => null,
+  buildAdapterConfig: () => ({}),
+};
+
+describe("adapter metadata", () => {
+  it("treats registered external adapters as enabled by default", () => {
+    expect(isEnabledAdapterType("external_test")).toBe(true);
+
+    expect(
+      listAdapterOptions((type) => type, [externalAdapter]),
+    ).toEqual([
+      {
+        value: "external_test",
+        label: "external_test",
+        comingSoon: false,
+        hidden: false,
+      },
+    ]);
+  });
+
+  it("keeps intentionally withheld built-in adapters marked as coming soon", () => {
+    expect(isEnabledAdapterType("process")).toBe(false);
+    expect(isEnabledAdapterType("http")).toBe(false);
+  });
+});