[Refactor] Extract OpenCode stall and steer-pickup watchdogs from harness

[roomote-roomote]

Created by Roomote. Follow up by mentioning @roomote-roomote or in the web UI.

Related issue

Follow-up maintainability cleanup from the stalled-model-stream fix in #166. No separate GitHub issue.

Why this PR exists

• A maintainer explicitly invited this PR in the linked issue or discussion
• I am a maintainer / this is internal Roomote work

What changed

Moved the OpenCode turn-stall and mid-turn steer-pickup timer subsystem out of the already-large OpenCodeServerHarness into a focused companion module. The harness keeps recovery actions (enqueue/prioritize/abort, transcript notices, and dispose/teardown hooks) and only arms/clears/notes activity through the coordinator. Defaults, timeouts, and silence/progress semantics are unchanged.

How it was tested

• pnpm exec dotenvx run -f .env.test -- pnpm --filter @roomote/worker exec vitest run src/sandbox-server/lib/harnesses/__tests__/opencode-server-stall-watchdogs.test.ts (10/10)
• Pre-push hooks: pnpm lint:fast, pnpm check-types:fast, pnpm knip

Checklist

• The PR title follows the repo convention: [Fix], [Feat], [Improve], [Refactor], [Docs], or [Chore] followed by a user-facing description
• This PR is small and scoped to one change
• pnpm lint and pnpm check-types pass locally
• I added tests or included a clear manual validation note above
• I removed secrets, tokens, private keys, and customer data from code, logs, and screenshots
• If this change should appear in the changelog, I ran pnpm changeset

[roomote-roomote]

No code issues found. This is a clean, behavior-preserving extraction of the stall/steer-pickup watchdogs; targeted tests (10/10) and worker typecheck pass. See task

_{Reviewed 6c2609d}