Enforce structured FormatId for creative formats

[bokelley]

Background

Previous versions of the AdCP schema allowed format_id to be a string. AdCP v2.4.1 requires format_id to be a structured object (FormatId) containing agent_url and id. This change ensures compliance by removing support for string-based format_ids and enforcing the structured object.

Changes

• src/creative_agent/schemas_generated/_schemas_v1_core_format_json.py: Updated Format.format_id to use the FormatId schema instead of str.
• src/creative_agent/data/standard_formats.py:
  • Created a create_format_id helper function to generate structured FormatId objects using the agent's URL.
  • Modified all format definitions to use create_format_id.
  • Updated get_format_by_id and filter_formats to correctly handle and filter by FormatId objects.
• src/creative_agent/server.py:
  • Updated list_creative_formats to convert input string format_ids to FormatId objects.
  • Modified preview_creative to use normalize_format_id_for_comparison for strict FormatId comparison, removing support for string format IDs.
• src/creative_agent/schemas/manifest.py: Changed PreviewCreativeRequest.format_id to strictly expect a FormatId object, removing the str option.
• tests/schema_compliance/test_format_schema_compliance.py: Updated test_output_format_ids_are_strings to verify that output_format_ids contain valid FormatId objects (dictionaries with agent_url and id), not strings.
• tests/smoke/test_server_startup.py: Updated test_list_creative_formats to correctly access the id field from FormatId objects.

Testing

• All existing tests pass (57/57).
• New formats created with create_format_id using the correct AGENT_URL.
• preview_creative correctly validates FormatId objects from manifests and requests.
• list_creative_formats correctly filters by structured FormatId objects.