fix(lint): resolve errcheck and unparam violations

Fixes CI lint failures by handling unchecked error returns and marking
unused parameters with blank identifiers.

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

internal/cmd/down.go

@@ -95,7 +95,7 @@ func runDown(cmd *cobra.Command, args []string) error {
 		if err != nil {
 			return fmt.Errorf("cannot proceed: %w", err)
 		}
-		defer lock.Unlock()
+		defer func() { _ = lock.Unlock() }()
 	}
 	allOK := true
 

internal/cmd/install.go

@@ -308,7 +308,7 @@ func runInstall(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
-func createMayorCLAUDEmd(mayorDir, townRoot string) error {
+func createMayorCLAUDEmd(mayorDir, _ string) error {
 	// Create a minimal bootstrap pointer instead of full context.
 	// Full context is injected ephemerally by `gt prime` at session start.
 	// This keeps the on-disk file small (<30 lines) per priming architecture.

internal/cmd/root.go

@@ -100,7 +100,7 @@ func warnIfTownRootOffMain() {
 // checkBeadsDependency verifies beads meets minimum version requirements.
 // Skips check for exempt commands (version, help, completion).
 // Deprecated: Use persistentPreRun instead, which calls CheckBeadsVersion.
-func checkBeadsDependency(cmd *cobra.Command, args []string) error {
+func checkBeadsDependency(cmd *cobra.Command, _ []string) error {
 	// Get the root command name being run
 	cmdName := cmd.Name()
 
@@ -142,7 +142,7 @@ func checkStaleBinaryWarning() {
 
 	if info.IsStale {
 		staleBinaryWarned = true
-		os.Setenv("GT_STALE_WARNED", "1")
+		_ = os.Setenv("GT_STALE_WARNED", "1")
 
 		msg := fmt.Sprintf("gt binary is stale (built from %s, repo at %s)",
 			version.ShortCommit(info.BinaryCommit), version.ShortCommit(info.RepoCommit))