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>

manifest.go

@@ -47,12 +47,6 @@ const manifest = JSON.parse(` + "`%s`" + `);
 export default manifest;
 `
 
-// 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"`
-}
-
 // LoadPluginManifest loads and parses the plugin.json file from the current directory.
 func LoadPluginManifest() (*model.Manifest, error) {
 	return LoadPluginManifestFromPath(".")