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/webapp_only_plugin.json

@@ -0,0 +1,9 @@
+{
+    "id": "com.example.webapponly", 
+    "name": "Webapp Only Plugin",
+    "description": "A plugin with only client-side code",
+    "version": "0.9.0",
+    "webapp": {
+        "bundle_path": "webapp/dist/bundle.js"
+    }
+}