feat: support codex custom tool type

[haoshan98]

Codex declares freeform tools such as apply_patch with type: "custom". Unlike function tools, these declarations can
include an opaque grammar, and their calls carry raw text in input rather than JSON in arguments. The typed Responses
path previously could not preserve that protocol through upstream inference, streaming, storage, and continuation.

• Add typed request, response, and input models for custom tool declarations, custom_tool_call items, and custom_tool_call_output results while preserving unknown format fields.
• Forward custom tool declarations to the upstream Responses endpoint without converting them to function tools.
• Accept and forward named custom tool_choice objects such as
  {"type":"custom","name":"apply_patch"} alongside existing function choices.
• Normalize and accumulate custom-tool streaming input events, return custom calls to the client for execution, and retain the call/output pair during stateful continuation.
• Keep custom calls client-owned in the shared tool loop while gateway-owned MCP and web-search calls continue to execute through their registered handlers.
• Persist terminal WebSocket responses before emitting completion so Codex can immediately continue a client-owned tool call without losing stored state when it closes the socket.
• Add custom-context coverage for the existing local WebSocket generate: false prewarm path, confirming that prompt
  and custom-tool declarations are preserved without upstream inference.
• Preserve and log structured upstream streaming failure details to make rejected tool requests diagnosable.
• Add an isolated catalog/cache seed helper that writes both Codex catalog files so freeform apply_patch remains
  available after the ordinary model cache expires, with canonical-path checks that keep writes inside /tmp.
• Extend the cassette recorder with custom-call continuation support and add direct-vLLM HTTP, gateway HTTP/SSE,
  gateway WebSocket, OpenAI HTTPS/SSE, and OpenAI WebSocket recordings that preserve raw input and
  custom_tool_call_output.
• Document direct gateway, codex exec, and interactive Codex verification workflows.