refactor: extract modular components from main.go

- Add internal/cli/validation.go for CLI flag validation
- Add internal/commands/hooks.go for hook management commands
- Add internal/commands/config.go for configuration commands
- Add internal/guide/guide.go for LLM usage guide
- Follows Go project layout standards for better maintainability

internal/cli/validation.go

@@ -0,0 +1,72 @@
+package cli
+
+import (
+	"fmt"
+
+	"github.com/carlosarraes/shush/internal/types"
+)
+
+func ValidateFlags(cli types.CLI) error {
+	hookCommands := []bool{
+		cli.InstallHook,
+		cli.UninstallHook,
+		cli.ListHooks,
+		cli.HookStatus,
+		cli.Config,
+		cli.CreateConfig,
+	}
+	hookFlagCount := 0
+	for _, flag := range hookCommands {
+		if flag {
+			hookFlagCount++
+		}
+	}
+
+	if hookFlagCount > 1 {
+		return fmt.Errorf("utility commands (--install-hook, --uninstall-hook, --list-hooks, --hook-status, --config, --create-config) are mutually exclusive")
+	}
+
+	if hookFlagCount > 0 {
+		if cli.Recursive || cli.Inline || cli.Block || cli.DryRun || cli.Backup || cli.Verbose {
+			return fmt.Errorf("hook commands cannot be combined with processing flags")
+		}
+
+		gitFlags := []bool{cli.ChangesOnly, cli.Staged, cli.Unstaged}
+		for _, flag := range gitFlags {
+			if flag {
+				return fmt.Errorf("hook commands cannot be combined with git flags")
+			}
+		}
+		return nil
+	}
+
+	gitFlags := []bool{cli.ChangesOnly, cli.Staged, cli.Unstaged}
+	gitFlagCount := 0
+	for _, flag := range gitFlags {
+		if flag {
+			gitFlagCount++
+		}
+	}
+
+	if gitFlagCount > 1 {
+		return fmt.Errorf("git flags (--changes-only, --staged, --unstaged) are mutually exclusive")
+	}
+
+	if gitFlagCount > 0 && cli.Path != "" {
+		return fmt.Errorf("cannot use git flags with explicit path argument")
+	}
+
+	if gitFlagCount > 0 && cli.Recursive {
+		return fmt.Errorf("cannot use git flags with --recursive (git handles repository scope)")
+	}
+
+	if gitFlagCount == 0 && cli.Path == "" {
+		return fmt.Errorf("path argument is required")
+	}
+
+	if cli.Inline && cli.Block {
+		return fmt.Errorf("--inline and --block flags are mutually exclusive")
+	}
+
+	return nil
+}