[codex] Add LLM observability guards

[Dreamstore2046]

Summary

• add LLM call counters and latency histograms with success/error labels
• log LLM failures as structured Pino events with event, model, latency_ms, requestId, and serialized error
• remove the remaining console.* use from agent/ and add an agent-specific ESLint no-console guard
• add a Prometheus alert for agent_llm_error_total / agent_llm_calls_total > 5% over 10 minutes
• document the new LLM observability metrics

Validation

• npm test -- shared/__tests__/metrics.test.ts agent/__tests__/llm-error-fallback.test.ts agent/__tests__/no-console.test.ts
• npm run lint:agent
• npx tsc --noEmit --target ES2022 --module ESNext --moduleResolution bundler --allowImportingTsExtensions --esModuleInterop --allowSyntheticDefaultImports --strict --skipLibCheck --types node,vitest shared/metrics.ts shared/__tests__/metrics.test.ts
• node -e "const fs=require('fs'); const yaml=require('js-yaml'); for (const f of ['docker/prometheus/prometheus.yml','docker/prometheus/alerts.yml']) { yaml.load(fs.readFileSync(f,'utf8')); } console.log('prometheus yaml ok')"
• git diff --cached --check

Notes:

• A broader focused tsc including agent/server.ts is still blocked by existing unrelated project errors in agent/tools.ts x402 template-literal arguments and shared/rate-limit.ts typings.
• docker compose config --quiet could not run in this local environment because Docker is not installed.

Closes #243.

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