feat: add --version flag to CLI

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

TODO.md

@@ -2,7 +2,6 @@
 
 ## Quick Wins
 
-- [ ] Add `--version` flag to the CLI
 - [ ] Check if revision exists before indexing (skip or require `--force`)
 
 ## Usability

cmd/nixos-options/main.go

@@ -14,12 +14,16 @@ import (
 	"git.t-juice.club/torjus/labmcp/internal/nixos"
 )
 
-const defaultDatabase = "sqlite://nixos-options.db"
+const (
+	defaultDatabase = "sqlite://nixos-options.db"
+	version         = "0.1.0"
+)
 
 func main() {
 	app := &cli.App{
 		Name:    "nixos-options",
 		Usage:   "MCP server for NixOS options search and query",
+		Version: version,
 		Flags: []cli.Flag{
 			&cli.StringFlag{
 				Name:    "database",