feat: expanded health checks, deploy filtering, per-project notifications, error sanitization, and audit trail

- Expand health endpoint to check DB, Docker, and NPM connectivity (FUNC-M4)
- Add project_id, stage_id, offset query params to deploys endpoint (FUNC-M5, FUNC-M6)
- Add notification_url field to Stage model for per-project overrides (FUNC-M2)
- Add NPM Ping method for health checking
- Sanitize all internal error messages in API handlers (SEC-M4)
- Add audit trail events for admin actions (FUNC-M3)
- Add EventLog event type to event bus

internal/store/models.go

@@ -25,9 +25,10 @@ type Stage struct {
 	Confirm      bool   `json:"confirm"`
 	EnableProxy  bool   `json:"enable_proxy"`
 	PromoteFrom  string `json:"promote_from"`
-	Subdomain    string `json:"subdomain"`
-	CreatedAt    string `json:"created_at"`
-	UpdatedAt    string `json:"updated_at"`
+	Subdomain       string `json:"subdomain"`
+	NotificationURL string `json:"notification_url"`
+	CreatedAt       string `json:"created_at"`
+	UpdatedAt       string `json:"updated_at"`
 }
 
 // Registry represents a container image registry.