[testing] Add scenario tests for DI lifecycle and request scope in real HTTP requests

[kang-heewon]

Problem

DI request scope is tested at the container level, but Croco also needs scenario tests proving the same lifecycle behavior inside real HTTP request handling.

Desired outcome

Request-scoped and singleton providers behave correctly across actual Node and Lambda request boundaries.

Acceptance criteria

• Add an HTTP fixture with singleton and request-scoped providers.
• Verify the same request reuses request-scoped instances where expected.
• Verify separate requests receive distinct request-scoped instances.
• Verify scope mismatch diagnostics during bootstrap or graph validation.
• Run the scenario through both Node/app fetch and Lambda handler paths.
• Include DI graph evidence in the test output where practical.