feat(crash): improve crash logging and mass death detection

Add comprehensive crash logging improvements to help diagnose mass session death events:

- Add TypeSessionDeath and TypeMassDeath event types for feed visibility
- Log pre-death events before killing sessions (who killed, why)
- Add mass death detection in daemon (3+ deaths in 30s triggers alert)
- Add macOS crash report check in gt doctor
- Support session death events in townlog and feed curator

Closes hq-kt1o6

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

internal/cmd/doctor.go

@@ -132,6 +132,7 @@ func runDoctor(cmd *cobra.Command, args []string) error {
 	d.Register(doctor.NewIdentityCollisionCheck())
 	d.Register(doctor.NewLinkedPaneCheck())
 	d.Register(doctor.NewThemeCheck())
+	d.Register(doctor.NewCrashReportCheck())
 
 	// Patrol system checks
 	d.Register(doctor.NewPatrolMoleculesExistCheck())