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/daemon/daemon_test.go

@@ -207,7 +207,7 @@ func TestSaveLoadState_Roundtrip(t *testing.T) {
 }
 
 // NOTE: TestIsWitnessSession removed - isWitnessSession function was deleted
-// as part of ZFC cleanup (gt-gaxo). Witness poking is now Deacon's responsibility.
+// as part of ZFC cleanup. Witness poking is now Deacon's responsibility.
 
 func TestLifecycleAction_Constants(t *testing.T) {
 	// Verify constants have expected string values