Add Claude Code CLI subprocess backend

[reed-nicolas]

Ports chia's ClaudeCodeLLM into SkyDiscover so runs can use a local claude CLI subscription instead of a hosted API. Three new files under skydiscover/llm/:

• claude_code_llm.py: subprocess wrapper around claude --print with NDJSON event streaming and typed error classification.
• claude_code_llm_pool.py: non-Ray subset of chia's exception hierarchy and rate-limit parsers.
• claude_code_adapter.py: factory that wires the backend onto LLMModelConfig.init_client so the existing LLMPool path picks it up.

Divergences from chia, all forced by the non-Ray bare-metal target:

• claude_path and claude_config_dir are constructor params so the binary and auth dir can be overridden via env vars at the caller.
• _get_node_id returns "local".
• Ray-coupled methods dropped (prompt_pooled, _serializable_config, _pooled_prompt_task, _session_transcript_path).
• Streaming _run_claude enforces timeout_seconds with proc.wait(timeout=...) plus kill-and-raise on expiry, since there is no Ray worker supervision to kill a stalled subprocess.
• ChiaTool type hints replaced with Any. Tools are unused here.

No behavior change for callers that do not set init_client.