feat(api): add APIFlask decorators to improve generated API spec doc

[tang-mm]

This PR enhances the Server API documentation using inline docstrings and decorators in v1.py, following APIFlask pattern. This improves the auto-generated OpenAPI spec with comprehensive documentation.

Description

API endpoint documentation migrated from server/API.md to v1.py:

• method docstring: the first line is "summary", followed by endpoint description text
• @v1.input and @v1.output decorators for request/response
• @v1.doc(responses={...}) decorators for non-200 status codes
• Moved parameter descriptions from docstrings to Schema metadata in schema.py

Schema definition:

• Added several new Marshmallow schemas for better explaining endpoint input and output
• Added field-level metadata descriptions to schemas

Resolved issues

CERTTF-780

Documentation

• OpenAPI spec (schemas/openapi.json) can be auto-generated using the functionality in docs(server): add OpenAPI spec generation and validation workflow #852
• API.md is no longer needed
  • Note: for /v1/client-permissions, both POST and PUT endpoints were described in the Markdown file, but only PUT is defined in v1.py

Web service API changes

API docstring and decorators are added or updated, no behavior changes.

Tests

Using the test introduced in #852 :

$ uvx --with tox-uv tox run -e schema