Replace raw JSON-RPC app-server protocol with @openai/codex-sdk.
The SDK wraps `codex exec` which ensures complete task execution per
turn, fixing the issue where app-server mode ended turns prematurely
(agent saying "하겠습니다" without doing the work).
Also fix AGENTS.md copy in agent-runner (was copying instructions.md
which Codex CLI doesn't read).
- Rewrite container-runner.ts to spawn node processes directly instead
of Docker/Apple Container
- Runner paths configurable via env vars (NANOCLAW_GROUP_DIR, etc.)
with container-path defaults for backwards compat
- Pass real credentials directly (no credential proxy needed)
- Remove ensureContainerSystemRunning() and startCredentialProxy()
from startup
- Add build:runners script for building agent-runner and codex-runner
- Fix TS strict mode errors in agent-runner ipc-mcp-stdio.ts
