Improve Codex output handling and long-response behavior

[chaz-working]

Summary

• use Codex CLI --output-last-message in exec mode and read from a temp file to capture the final assistant message cleanly
• strip terminal control sequences from stdout/stderr fallback output
• avoid duplicate promise resolution in process finalization
• replace output truncation in Telegram handler with a clear message when response exceeds MAX_OUTPUT_CHARS

Validation

• npm run typecheck