feat: integrate AgentRQ task manager plugin

- Clone agentrq/agentrq plugin to plugins/agentrq/
- Update package.json name to 'agentrq'
- Add agentrq plugin to tauri.conf.json resources
- Add AGENTRQ_PACKAGE constant and bundled_agentrq_plugin() discovery
- Add install_agentrq_plugin() function to modlens.rs
- Update README with plugin listing

plugins/agentrq/tsdown.config.ts

@@ -0,0 +1,16 @@
+import { defineConfig } from 'tsdown'
+
+// `prepare` runs this after a git install, where the consumer has no project
+// references and no type-check context. Keep the build self-contained: bundle
+// `src/` to `lib/`, emit declarations, and leave every peer/runtime dependency
+// external so the harness supplies its own copies.
+export default defineConfig({
+  entry: ['src/index.ts'],
+  outDir: 'lib',
+  format: ['esm'],
+  platform: 'node',
+  target: 'node20',
+  dts: true,
+  clean: true,
+  external: [/^@deepseek-ai\//, /^@modelcontextprotocol\//],
+})