feat: add dynamic log level adjustment APIs (#13850)

Add REST APIs to dynamically query and modify log levels at runtime for
both Python (Flask) and Go servers.

Changes:
- common/log_utils.py: add set_log_level() and get_log_levels()
functions
- admin/server/routes.py: add GET/PUT /api/v1/admin/log_levels endpoints
- api/apps/system_app.py: add GET/PUT /api/{version}/system/log_levels
endpoints
- internal/logger/logger.go: add GetLevel() and SetLevel() with atomic
level support
- internal/handler/system.go: add GetLogLevel, SetLogLevel, Health
handlers
- internal/router/router.go: route /health to systemHandler
- internal/admin/handler.go: add GetLogLevel, SetLogLevel handlers
- internal/admin/router.go: add /api/v1/admin/log_level routes

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

admin/server/routes.py

@@ -30,6 +30,7 @@ from roles import RoleMgr
 from api.common.exceptions import AdminException
 from common.versions import get_ragflow_version
 from api.utils.api_utils import generate_confirmation_token
+from common.log_utils import get_log_levels, set_log_level
 
 admin_bp = Blueprint("admin", __name__, url_prefix="/api/v1/admin")
 
@@ -652,3 +653,39 @@ def test_sandbox_connection():
         return error_response(str(e), 400)
     except Exception as e:
         return error_response(str(e), 500)
+
+
+@admin_bp.route("/log_levels", methods=["GET"])
+@login_required
+@check_admin_auth
+def get_logger_levels():
+    """Get current log levels for all packages."""
+    try:
+        res = get_log_levels()
+        return success_response(res, "Get log levels", 0)
+    except Exception as e:
+        return error_response(str(e), 500)
+
+
+@admin_bp.route("/log_levels", methods=["PUT"])
+@login_required
+@check_admin_auth
+def set_logger_level():
+    """Set log level for a package."""
+    try:
+        data = request.get_json()
+        if not data or "pkg_name" not in data or "level" not in data:
+            return error_response("pkg_name and level are required", 400)
+
+        pkg_name = data["pkg_name"]
+        level = data["level"]
+        if not isinstance(pkg_name, str) or not isinstance(level, str):
+            return error_response("pkg_name and level must be strings", 400)
+
+        success = set_log_level(pkg_name, level)
+        if success:
+            return success_response({"pkg_name": pkg_name, "level": level}, "Log level updated successfully")
+        else:
+            return error_response(f"Invalid log level: {level}", 400)
+    except Exception as e:
+        return error_response(str(e), 500)