[EPAC-743]: Display government's official tabled response for petitions

[riddim-developer-bot]

Summary

This PR implements the iOS-side feature to display the government's official tabled response to a petition on the petition detail screen (PetitionDetailView), fulfilling the EPAC-743 requirements.

Changes:

• Entities / Models: Extended EPetition model with an optional governmentResponse: PetitionGovernmentResponse value object.
• Ports: Created PetitionGovernmentResponseQueryPort to define the boundary for fetching a petition's government response.
• Adapters:
  • Implemented BackendPetitionGovernmentResponseQueryPort which fetches the response from the backend endpoint: GET /api/v1/petitions/{id}/response.
  • Added a "Government Response" section to PetitionDetailView that displays when a response is present (showing the tabled date, responding minister/department, and verbatim response text).
  • Handles the qualified/awaiting response state (displaying "Awaiting government response" for petitions with >= 500 signatures) and the did-not-qualify state.
• Documentation: Updated the use-case-catalog.md with the new entities, ports, and the LoadPetitionGovernmentResponse use case.
• Tests:
  • Added unit tests for the use case LoadPetitionGovernmentResponseTests.
  • Added integration/unit tests for the adapter BackendPetitionGovernmentResponseQueryPortTests using mock protocols.
  • Added snapshot tests in SnapshotTests covering all three visual states (withResponse, awaitingResponse, notQualified) and committed the reference snapshot images.

JSON Contract

{
  "text": "String",
  "tabled_on": "YYYY-MM-DD",
  "responding_minister": "String?"
}

Verification

• Local unit tests build and run successfully:
  • make test TEST_ONLY=LoadPetitionGovernmentResponseTests
  • make test TEST_ONLY=BackendPetitionGovernmentResponseQueryPortTests
• Snapshot tests compile and successfully generate comparison reference images:
  • make test TEST_ONLY=SnapshotTests
• Working copy status is verified clean with git status --porcelain.