#21004: feat(runtime): enable loop detection by default + support timeout=0

## Summary - enable tool-loop detection by default - allow `agents.defaults.timeoutSeconds = 0` to represent no-timeout (timer-safe max delay internally) - align gateway timeout parsing and tests with new timeout semantics - update config schema/help/docs (including zh-CN docs) for new defaults ## Why This reduces runaway tool-loop incidents out of the box and makes timeout behavior explicit and consistent across runtime + gateway paths. ## Validation - `pnpm vitest run --config vitest.unit.config.ts src/agents/tool-loop-detection.test.ts src/agents/subagent-depth.test.ts` - `pnpm vitest run --config vitest.e2e.config.ts src/commands/agent-via-gateway.e2e.test.ts`