fix(commandcode): retry on transient stream error and avoid fake stop chunks

[Christian-Gennari]

Closes #4129

Summary

Improves CommandCode upstream reliability by automatically retrying transient server connection drops, preventing mid-stream errors from emitting fake stop chunks to clients, and ensuring assistant turns with tool calls pass reasoning blocks.

To be clear, the primary root cause for the connection drops is upstream instability on CommandCode's own infrastructure (tracked in CommandCodeAI/command-code#597). This PR provides defensive resiliency on 9Router's side so downstream clients do not experience interrupted turns while CommandCode resolves their backend stability.

Details

• Automatic retry on initial drops: CommandCodeExecutor.execute() retries upstream up to 2 times with backoff when inspectAndWrapCommandCodeResponse returns 502/503/504 status codes.
• Mid-stream error termination: commandcode-to-openai.js now throws on upstream error events instead of emitting [CommandCode error: ...] followed by finish_reason: "stop", preventing clients from treating server disconnects as valid completions.
• Reasoning block in assistant requests: openai-to-commandcode.js includes reasoning blocks for assistant messages with tool calls or thought content to comply with upstream thinking mode expectations.
• Tests: Extended tests/unit/commandcode-executor.test.js to verify retry recovery and status handling.

[decolua]

Thanks @Christian-Gennari for the contribution! Reviewed and merged into master. 🙏