Add tools command for direct binary downloads from GitHub releases

Introduces a new 'tools' command that installs development tools (golangci-lint, gotestsum)
by downloading pre-built binaries directly from GitHub releases instead of using 'go get -tool'.
This prevents modifications to plugin go.mod files and improves build reliability.

Features:
- Cross-platform support (Windows, macOS, Linux) with automatic architecture detection
- Version-specific binary naming with symlinks for easy access
- Configurable installation directory via --bin-dir flag
- Tar.gz archive extraction with binary validation
- Updated Makefile integration to use downloaded binaries

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

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

pluginctl.go

@@ -17,6 +17,12 @@ const (
 	UnknownVersion = "unknown"
 )
 
+// PluginCtlConfig represents the configuration for pluginctl stored in the manifest props.
+type PluginCtlConfig struct {
+	Version      string   `json:"version,omitempty"`
+	IgnoreAssets []string `json:"ignore_assets,omitempty"`
+}
+
 // IsValidPluginDirectory checks if the current directory contains a valid plugin.
 func IsValidPluginDirectory() error {
 	_, err := LoadPluginManifest()