fix: Address golangci-lint errors (errcheck, gosec) (#76)

Apply PR #76 from dannomayernotabot:

- Add golangci exclusions for internal package false positives
- Tighten file permissions (0644 -> 0600) for sensitive files
- Add ReadHeaderTimeout to HTTP server (slowloris prevention)
- Explicit error ignoring with _ = for intentional cases
- Add //nolint comments with justifications
- Spelling: cancelled -> canceled (US locale)

Co-Authored-By: dannomayernotabot <noreply@github.com>

🤖 Generated with Claude Code

internal/cmd/hook.go

@@ -114,7 +114,7 @@ func runHookOrStatus(cmd *cobra.Command, args []string) error {
 	return runHook(cmd, args)
 }
 
-func runHook(cmd *cobra.Command, args []string) error {
+func runHook(_ *cobra.Command, args []string) error {
 	beadID := args[0]
 
 	// Polecats cannot hook - they use gt done for lifecycle