Allow parent worker instruction bridge

[pmbstyle]

Summary

• Allow the runtime bridge to accept the answer_worker_instruction tool injected for parent-capable workers.
• Keep answer_worker_instruction blocked for workers that cannot spawn children.
• Add a regression test covering the bridge validation boundary.

Why

Parent workers with start_child_worker / start_workers_parallel already receive an injected answer_worker_instruction tool in the agent loop, but the Octo-side bridge still validated calls against the original template available_tools. In production this made a research_coordinator unable to answer a child instruction, after which it burned steps polling child results.

Validation

• uv run pytest -q tests/test_agent_loop_improvements.py tests/test_worker_suspend_resume.py tests/test_worker_child_spawning.py
• uv run ruff check src/octopal/runtime/workers/runtime.py tests/test_agent_loop_improvements.py
• uv run pytest -q