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/daemon/notification.go

@@ -165,7 +165,7 @@ func (m *NotificationManager) MarkSessionActive(session string) error {
 			ns.Consumed = true
 			ns.ConsumedAt = time.Now()
 			if data, err := json.Marshal(&ns); err == nil {
-				_ = os.WriteFile(path, data, 0644)
+				_ = os.WriteFile(path, data, 0644) // non-fatal: state file update
 			}
 		}
 	}
@@ -198,7 +198,7 @@ func (m *NotificationManager) ClearStaleSlots() error {
 		}
 
 		if time.Since(info.ModTime()) > m.maxAge {
-			_ = os.Remove(path)
+			_ = os.Remove(path) // best-effort cleanup
 		}
 	}