Refactor system API (#13958)

### What problem does this PR solve?

- ping
- token
- log level

### Type of change

- [x] Refactoring


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Refactor**
* System endpoints consolidated under /api/v1/system: ping, health
check, and token management moved to the centralized API surface.
* Token management unified at /api/v1/system/tokens with
list/create/delete behavior.

* **Documentation**
  * API reference updated to reflect the new /api/v1/system paths.

* **Tests**
* Client fixtures and test utilities updated to use
/api/v1/system/tokens; one unit test for health/oceanbase status
removed.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

web/src/utils/api.ts

@@ -171,9 +171,9 @@ export default {
 
   // system
   getSystemVersion: `${restAPIv1}/system/version`,
-  getSystemTokenList: `${webAPI}/system/token_list`,
-  createSystemToken: `${webAPI}/system/new_token`,
-  removeSystemToken: `${webAPI}/system/token`,
+  getSystemTokenList: `${restAPIv1}/system/tokens`,
+  createSystemToken: `${restAPIv1}/system/tokens`,
+  removeSystemToken: `${restAPIv1}/system/tokens`,
   getSystemConfig: `${webAPI}/system/config`,
   setLangfuseConfig: `${webAPI}/langfuse/api_key`,