fix: merge PR #562 — MCP session management, Claude passthrough, OAuth modal, detectFormat fixes

Cherry-pick from codex/omniroute-fixes-20260324:
- Replace MCP singleton transport with per-session architecture for Streamable HTTP
- Fix Claude passthrough via OpenAI round-trip normalization
- Add detectFormatFromEndpoint() for endpoint-aware format detection
- Support raw code#state in OAuth modal for Claude Code remote auth
- Expose cloudConfigured/cloudUrl/machineId in settings API
- Switch docker-compose.prod.yml target to runner-cli
- Add 3 new tests for round-trip and detectFormat

PR: #562

docker-compose.prod.yml

@@ -16,7 +16,7 @@ services:
     container_name: omniroute-prod
     build:
       context: .
-      target: runner-base
+      target: runner-cli
     image: omniroute:prod
     restart: unless-stopped
     env_file: .env