Mount worker skill state at workspace root

[pmbstyle]

Summary

• mount shared worker skill directories at the canonical Docker workspace root
• keep worker-local compatibility mounts for the same directories
• cover both skills registry state and skill runtime env state in launcher tests

Root cause

PR #103 moved Docker workers to use the shared workspace root as OCTOPAL_WORKSPACE_DIR. The worker process runs as a non-root user, while /workspace itself is owned by the container image. The launcher mounted skills only under the worker directory, so code that initializes workspace-level skill state tried to create /workspace/skills and later /workspace/.skill-envs directly inside the root-owned mount point.

Validation

• uv run pytest tests\test_worker_launcher_isolation.py tests\test_filesystem_hardening.py tests\test_worker_router.py tests\test_agent_worker_contracts.py
• production hotfix smoke: Docker worker can initialize /workspace/skills and /workspace/.skill-envs
• production scheduled Moltbook worker now passes worker initialization and runs child workers instead of failing before task execution