fix: adopt codex-plugin-cc reliability guards

[nillo]

Summary

Adopts the verified ContextRelay-relevant reliability patterns from openai/codex-plugin-cc without porting its plugin architecture or UX. This bounds backup timeout cleanup, daemon shutdown cleanup, and long-running Codex turns.

Changes

• Add backup-agent timeout escalation: SIGTERM first, then SIGKILL after CONTEXTRELAY_BACKUP_KILL_GRACE_MS, with backup_timeout ledger telemetry.
• Add bounded daemon shutdown steps via runShutdownSteps, with daemon_shutdown runtime event telemetry and CONTEXTRELAY_DAEMON_SHUTDOWN_STEP_TIMEOUT_MS.
• Add a per-turn wall-clock Codex watchdog via CONTEXTRELAY_TURN_MAX_MS, status/viewer exposure for the last watchdog fire, and turn_watchdog runtime events.
• Document the new reliability guards and environment variables in the README.
• Rebuild CLI/plugin bundles.

Upstream References

• Zombie running job blocks all subsequent task calls when process crashes openai/codex-plugin-cc#202
• Review jobs stuck in 'running' after process death — no dead-PID detection openai/codex-plugin-cc#164
• sendBrokerShutdown has no timeout — SessionEnd hook can hang indefinitely openai/codex-plugin-cc#288
• Claude Code review hangs on MCP tool call when an MCP server triggers elicitation openai/codex-plugin-cc#258
• fix(runtime): add wall-clock timeouts to JSON-RPC request and captureTurn openai/codex-plugin-cc#302
• feat(codex): per-turn watchdog with TurnWatchdogError + exit 124 openai/codex-plugin-cc#312

Testing

• bun test src/unit-test/backup-runner.test.ts src/unit-test/shutdown.test.ts src/unit-test/codex-adapter.test.ts
• bun run typecheck
• bun run build:cli && bun run build:plugin
• bun run check → 322 pass, 0 fail, 999 expect() calls; bundle sync, plugin version, and lockfile checks passed