[codex] fix gateway request cleanup and model listing

[WindoC]

Summary

Fix gateway request lifecycle handling and Docker packaging issues found while verifying issue #2.

Changes include:

• Bound /v1/models SDK discovery with CODEBUDDY_GATEWAY_MODELS_TIMEOUT, falling back to the gateway model list when discovery hangs.
• Add request body size enforcement and cleanup of request abort/close listeners.
• Guard response writes after client disconnects.
• Normalize CRLF shell scripts during Docker build so Linux shebangs work from Windows checkouts.
• Update tests and docs for the new behavior and verification flow.

Validation

• npm test from gateway/: passed, 10/10
• node --check gateway/server.mjs: passed
• Local API verification passed for /health, /v1/models, non-streaming chat, custom tool calls, tool-result continuation, and streaming SSE
• Docker build passed for codebuddy-gateway:custom-tool-supported
• Container API verification passed for /health, /v1/models, non-streaming chat, custom tool calls, tool-result continuation, and streaming SSE

Closes #2