chore(gastown): drop unused promise param from unhandledRejection handler

[jrf0110]

Follow-up to #3072. Toast removed String(promise) (the no-base-to-string lint error) but left the promise parameter declared, tripping a different lint rule:

Parameter 'promise' is declared but never used. Unused parameters should start with a '_'.

Drops the parameter entirely. Also removes the now-redundant event: 'unhandled_rejection' field from the log payload — the log key (container.unhandled_rejection) already conveys that.

Unblocks PR #2974 (gastown-staging → main promote).

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (1 files)

• services/gastown/container/src/main.ts

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_{Reviewed by gpt-5.5-20260423 · 89,579 tokens}