fix(openai): reserialize response body when MCP approval is required (#839)

[Artemon-line]

Summary

When an MCP tool call requires approval, McpDispatchFilter::on_response_body detects the approval requirement, constructs an mcp_approval_request item, and appends it to state.accumulated_output. However, because AgenticLoopFilter had already formatted the HTTP response body before McpDispatchFilter ran, and McpDispatchFilter had read-only response body access, the mcp_approval_request event was missing from the serialized HTTP client response.

This change:

1. Gives McpDispatchFilter read-write response body access (BodyAccess::ReadWrite).
2. Exposes finalize_response_body on ResponsesState to re-serialize the response body from accumulated_output and usage.
3. Calls state.finalize_response_body(body) inside handle_approval_required when appending an approval request event.
4. Updates AgenticLoopFilter calls to use state.finalize_response_body(body).
5. Adds a unit test verifying that mcp_approval_request is correctly serialized into the returned HTTP response body bytes.

Related issue

Closes #839

Validation

• Unit tests: cargo test -p praxis-ai-apis -- mcp_dispatch::tests
• Workspace tests: make test
• make lint and make fmt

Checklist

• I reviewed every changed line and can explain the change.
• New capabilities include an example config and functional example test. (N/A — bug fix)
• User-facing behavior and generated documentation are updated. (N/A)
• Performance-sensitive changes include appropriate benchmark or load-test evidence. (N/A)
• Commits are signed and include a Signed-off-by trailer.

Breaking changes

None.

[leseb]

@Artemon-line next time use your fork. Thanks

[leseb]

all those changes are not needed and unrelated to the main fix. this is just cosmetic

[leseb]

since this now mutates the body, you must udated the body access mode to ReadWrite