Implement RFC 9457 compliant error response for ti_run endpoint

[MonsterChenzhuo]

Description

This PR implements RFC 9457 (Problem Details for HTTP APIs) compliant error responses for the ti_run endpoint in the Execution API, addressing the TODO left in the code.

When a Task Instance cannot be marked as running (e.g., due to an invalid state), the API now returns a structured error response containing standard fields like type , title , status , detail , and instance , while preserving existing context fields.

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[henry3260]

Should we standardize all HTTP responses in task_instances.py to follow RFC 9457?