Document intentional error suppressions with comments (gt-zn9m)

All 156 instances of _ = error suppression in non-test code now have
explanatory comments documenting why the error is intentionally ignored.

Categories of intentional suppressions:
- non-fatal: session works without these - tmux environment setup
- non-fatal: theming failure does not affect operation - visual styling
- best-effort cleanup - defer cleanup on failure paths
- best-effort notification - mail/notifications that should not block
- best-effort interrupt - graceful shutdown attempts
- crypto/rand.Read only fails on broken system - random ID generation
- output errors non-actionable - fmt.Fprint to io.Writer

This addresses the silent failure and debugging concerns raised in the
issue by making the intentionality explicit in the code.

Generated with Claude Code https://claude.com/claude-code

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

internal/witness/manager.go

@@ -83,7 +83,7 @@ func (m *Manager) Status() (*Witness, error) {
 		if !processExists(w.PID) {
 			w.State = StateStopped
 			w.PID = 0
-			_ = m.saveState(w)
+			_ = m.saveState(w) // non-fatal: state file update
 		}
 	}
 
@@ -127,7 +127,7 @@ func (m *Manager) Stop() error {
 
 	// If we have a PID, try to stop it gracefully
 	if w.PID > 0 && w.PID != os.Getpid() {
-		// Send SIGTERM
+		// Send SIGTERM (best-effort graceful stop)
 		if proc, err := os.FindProcess(w.PID); err == nil {
 			_ = proc.Signal(os.Interrupt)
 		}