Add manifest command with subcommands for plugin information

- Add manifest command with id, version, has_server, has_webapp subcommands
- Provides simple text output for easy parsing/scripting
- Update help documentation with usage examples
- Follow existing command patterns and architecture

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

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

manifest.go

@@ -0,0 +1,50 @@
+package pluginctl
+
+import (
+	"fmt"
+	"path/filepath"
+)
+
+// RunManifestCommand implements the 'manifest' command functionality with subcommands.
+func RunManifestCommand(args []string, pluginPath string) error {
+	if len(args) == 0 {
+		return fmt.Errorf("manifest command requires a subcommand: id, version, has_server, has_webapp")
+	}
+
+	// Convert to absolute path
+	absPath, err := filepath.Abs(pluginPath)
+	if err != nil {
+		return fmt.Errorf("failed to resolve path: %w", err)
+	}
+
+	// Load plugin manifest
+	manifest, err := LoadPluginManifestFromPath(absPath)
+	if err != nil {
+		return fmt.Errorf("failed to load plugin manifest: %w", err)
+	}
+
+	subcommand := args[0]
+	switch subcommand {
+	case "id":
+		fmt.Println(manifest.Id)
+	case "version":
+		fmt.Println(manifest.Version)
+	case "has_server":
+		if HasServerCode(manifest) {
+			fmt.Println("true")
+		} else {
+			fmt.Println("false")
+		}
+	case "has_webapp":
+		if HasWebappCode(manifest) {
+			fmt.Println("true")
+		} else {
+			fmt.Println("false")
+		}
+	default:
+		return fmt.Errorf("unknown subcommand: %s. Available subcommands: id, version, has_server, has_webapp",
+			subcommand)
+	}
+
+	return nil
+}