refactor(api): migrate console message responses from marshal_with to BaseModel

[ai-hpc]

Part of #28015

Summary

Extract message response schemas from inline Flask-RESTX api.model(...)/@marshal_with into Pydantic BaseModel classes and register them with register_schema_models(). Keep response compatibility by mapping re_sign_file_url_answer -> answer, message_metadata_dict -> metadata, and normalizing datetime/file-contained fields.

Checklist

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran make lint and make type-check (backend) and cd web && pnpm exec vp staged (frontend) to appease the lint gods

[github-actions]

Pyrefly Diff

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[Copilot]

Pull request overview

Refactors the console message endpoints to stop using inline Flask-RESTX api.model(...) / @marshal_with response definitions and instead serialize responses via Pydantic models registered with register_schema_models(), while preserving key field mappings and normalization.

Changes:

• Introduces MessageDetailResponse and MessageInfiniteScrollPaginationResponse Pydantic response models (with alias normalization + timestamp conversion).
• Updates chat-message list and message-detail endpoints to return model_dump(mode="json") output instead of relying on @marshal_with.
• Adds a unit test covering alias normalization (re_sign_file_url_answer → answer, message_metadata_dict → metadata) and datetime → unix timestamp conversion.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
api/controllers/console/app/message.py	Replaces RESTX marshal models with registered Pydantic response models and uses Pydantic serialization in endpoints.
api/tests/unit_tests/controllers/console/app/test_message_api.py	Adds unit coverage for new MessageDetailResponse alias + timestamp normalization behavior.

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