Clean up stale issue references in comments (gt-z5bri)

- daemon.go: Update gt-2hzl4 comment to past tense (timeout fallback is implemented)
- lifecycle.go: Remove "to be removed" promise for gt-psuw7 (code stays)
- keepalive_test.go: Remove tombstoned gt-gaxo epic reference
- doctor.go: Remove tombstoned gt-gaxo epic reference
- daemon_test.go: Remove tombstoned gt-gaxo epic reference

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/keepalive/keepalive_test.go

@@ -61,7 +61,6 @@ func TestStateAge(t *testing.T) {
 
 	// NOTE: IsFresh(), IsStale(), IsVeryStale() were removed as part of ZFC cleanup.
 	// Staleness classification belongs in Deacon molecule, not Go code.
-	// See gt-gaxo epic for rationale.
 }
 
 func TestDirectoryCreation(t *testing.T) {