fix(tui): preserve worker rejection handling

[rekram1-node]

Summary

• restore the TUI backend worker unhandledRejection listener removed during the Effect logging migration
• log rejected worker callbacks through the Effect observability layer instead of allowing Bun to terminate the worker
• dispose the dedicated logging runtime during worker shutdown

Context

After the listener was removed in c06ad7c88, an unhandled rejection in an async worker callback can terminate the backend worker. Subsequent TUI requests then surface only Worker has been terminated, hiding the original rejection.

A reported original rejection is:

Error: Cannot call write after a stream was destroyed
    at _write (internal:streams/writable:240:29)
    at write (/$bunfs/root/chunk-jv1w06hr.js:32:14071)
    at doWrite (/$bunfs/root/chunk-jv1w06hr.js:4:1687)
    at processTicksAndRejections (native:7:39)

This indicates a separate stream teardown race. This PR restores rejection containment and observability; it does not claim to fix that underlying stream lifecycle bug.

Closes #33269
Closes #32694

Verification

• bun typecheck from packages/opencode
• git diff --check