Go: add OceanBase /system/oceanbase/status endpoint with live health probe

[kinjitakabe]

Go: add OceanBase /system/oceanbase/status endpoint with live health probe

What

Ports the Python GET /api/v1/system/oceanbase/status endpoint to the Go server. The endpoint connects to OceanBase over the MySQL wire protocol and reports live health + performance metrics.

Changes

• internal/service/oceanbase_probe.go (new) — a database/sql MySQL-wire probe gathering health (uri, version_comment) and performance metrics (latency_ms, active_connections, max_connections, slow_queries, storage_used/total). Mirrors Python OBConnection.health() + get_performance_metrics(). Each metric query is isolated so a missing OB-specific table/variable degrades gracefully instead of failing the whole probe.
• internal/service/system.go — GetOceanbaseStatus() runs the probe, gated on the oceanbase config section being present (rather than DOC_ENGINE==oceanbase), so health is observable while ES/Infinity remain the active doc engine. No config → the Python-parity "OceanBase is not in use." path.
• internal/handler/system.go — OceanbaseStatus handler returning the Python-parity envelope: HTTP 200 / code 0 on success, HTTP 200 / code 500 with data.status="error" when unconfigured.
• internal/router/router.go — registers GET /api/v1/system/oceanbase/status in the authenticated system group.

Verification

Deployed the full Go stack locally (ES + MySQL + Redis + MinIO + admin_server + ragflow_server) against a running OceanBase (SeekDB) 4.3.5.3 instance, logged in through the web UI, and hit the endpoint from the live session:

{
  "code": 0,
  "data": {
    "status": "alive",
    "message": {
      "health": { "uri": "localhost:2881", "version_comment": "OceanBase 4.3.5.3 seekdb (r1.3.0.0)" },
      "performance": {
        "connection": "connected", "latency_ms": 9.759,
        "active_connections": 2, "max_connections": "2147483647",
        "slow_queries": 0, "storage_used": "N/A", "storage_total": "N/A"
      }
    }
  },
  "message": "success"
}

Live response rendered from the logged-in RAGFlow browser session → Go backend → OceanBase:

Also verified: unauthenticated requests return 401; missing config returns the code 500 "not in use" envelope.

Notes

• Local deploy-only edits (conf/service_conf.yaml, web/package-lock.json) are intentionally excluded from this PR.
• storage_* reports N/A against SeekDB (empty doc DB + no oceanbase.__all_disk_stat); full OceanBase populates these — the graceful fallback matches the Python reference.