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/boot.go

@@ -277,10 +277,7 @@ func runDegradedTriage(b *boot.Boot) (action, target string, err error) {
 	tm := b.Tmux()
 
 	// Check if Deacon session exists
-	deaconSession, err := getDeaconSessionName()
-	if err != nil {
-		return "error", "deacon", fmt.Errorf("getting deacon session name: %w", err)
-	}
+	deaconSession := getDeaconSessionName()
 	hasDeacon, err := tm.HasSession(deaconSession)
 	if err != nil {
 		return "error", "deacon", fmt.Errorf("checking deacon session: %w", err)