feat(health): add health checking endpoints and logic

Introduce health checking functionality with liveness and readiness 
endpoints to monitor the application's status. Implement a health 
checker that verifies database connectivity and provides a simple 
liveness check. Update service routing to use the new health 
checker functionality. Add corresponding unit tests for validation.

go.mod

@@ -4,6 +4,7 @@ go 1.25
 
 require (
 	github.com/99designs/gqlgen v0.17.83
+	github.com/DATA-DOG/go-sqlmock v1.5.2
 	github.com/Khan/genqlient v0.8.1
 	github.com/alecthomas/kong v1.13.0
 	github.com/apex/log v1.9.0