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/server_only_plugin.json

@@ -0,0 +1,13 @@
+{
+    "id": "com.example.serveronly",
+    "name": "Server Only Plugin",
+    "description": "A plugin with only server-side code",
+    "version": "1.5.0",
+    "min_server_version": "8.0.0",
+    "server": {
+        "executables": {
+            "linux-amd64": "server/dist/plugin-linux-amd64",
+            "darwin-amd64": "server/dist/plugin-darwin-amd64"
+        }
+    }
+}