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/status.go

@@ -469,7 +469,7 @@ func outputStatusText(status TownStatus) error {
 }
 
 // renderAgentDetails renders full agent bead details
-func renderAgentDetails(agent AgentRuntime, indent string, hooks []AgentHookInfo, townRoot string) {
+func renderAgentDetails(agent AgentRuntime, indent string, hooks []AgentHookInfo, townRoot string) { //nolint:unparam // indent kept for future customization
 	// Line 1: Agent bead ID + status
 	// Reconcile bead state with tmux session state to surface mismatches
 	// States: "running" (active), "idle" (waiting), "stopped", "dead", etc.
@@ -646,8 +646,8 @@ func discoverRigHooks(r *rig.Rig, crews []string) []AgentHookInfo {
 // allHookBeads is a preloaded map of hook beads for O(1) lookup.
 func discoverGlobalAgents(allSessions map[string]bool, allAgentBeads map[string]*beads.Issue, allHookBeads map[string]*beads.Issue, mailRouter *mail.Router, skipMail bool) []AgentRuntime {
 	// Get session names dynamically
-	mayorSession, _ := getMayorSessionName()
-	deaconSession, _ := getDeaconSessionName()
+	mayorSession := getMayorSessionName()
+	deaconSession := getDeaconSessionName()
 
 	// Define agents to discover
 	agentDefs := []struct {