Initial implementation of pluginctl CLI tool

- Add comprehensive info command with plugin manifest parsing -
Implement global --plugin-path flag and PLUGINCTL_PLUGIN_PATH env var -
Add full test suite with fixtures for various plugin configurations -
Set up build system with Makefile, goreleaser, and golangci-lint -
Include development tools with pinned versions for reproducible builds

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

testdata/plugin.json

@@ -0,0 +1,22 @@
+{
+  "id": "com.example.testplugin",
+  "name": "Test Plugin",
+  "description": "A test plugin for demonstrating pluginctl functionality",
+  "version": "1.0.0",
+  "min_server_version": "7.0.0",
+  "server": {
+    "executables": {
+      "linux-amd64": "server/dist/plugin-linux-amd64",
+      "darwin-amd64": "server/dist/plugin-darwin-amd64",
+      "windows-amd64": "server/dist/plugin-windows-amd64.exe"
+    }
+  },
+  "webapp": {
+    "bundle_path": "webapp/dist/main.js"
+  },
+  "settings_schema": {
+    "header": "Configure the Test Plugin",
+    "footer": "",
+    "settings": []
+  }
+}