feat(slackbotv2): show Codex effort and speed

[decofe]

Summary

• show effective Codex reasoning effort and service-tier speed in the first Slack response context line
• honor per-turn -rsn and deployment-level effort overrides
• mirror the deployment effort setting into slackbotv2 and cover default rendering

Testing

• bun test test/console-session-link.test.ts
• bun test test/chat-sdk-emulate.test.ts -t "appends an Open-session|shows the harness default model"
• bun run check:types
• git diff --check

Prompted by: @snario

Rebased replacement for #1068.

Prompted by: @snario