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>

api/apps/system_app.py

@@ -31,6 +31,7 @@ from api.utils.api_utils import (
 )
 from common.versions import get_ragflow_version
 from common.time_utils import current_timestamp, datetime_format
+from common.log_utils import get_log_levels, set_log_level
 from timeit import default_timer as timer
 
 from rag.utils.redis_conn import REDIS_CONN
@@ -375,3 +376,56 @@ def get_config():
         "registerEnabled": settings.REGISTER_ENABLED,
         "disablePasswordLogin": settings.DISABLE_PASSWORD_LOGIN,
     })
+
+
+@manager.route("/log_levels", methods=["GET"])  # noqa: F821
+@login_required
+async def get_logger_levels():
+    """
+    Get current log levels for all packages.
+    ---
+    tags:
+        - System
+    responses:
+        200:
+            description: Return current log levels
+    """
+    return get_json_result(data=get_log_levels())
+
+
+@manager.route("/log_levels", methods=["PUT"])  # noqa: F821
+@login_required
+async def set_logger_level():
+    """
+    Set log level for a package.
+    ---
+    tags:
+        - System
+    parameters:
+        - in: body
+          name: body
+          required: true
+          schema:
+            type: object
+            properties:
+                pkg_name:
+                    type: string
+                    description: Package name (e.g., "rag.utils.es_conn")
+                level:
+                    type: string
+                    description: Log level (DEBUG, INFO, WARNING, ERROR)
+    responses:
+        200:
+            description: Log level updated successfully
+    """
+    from quart import request
+    data = await request.get_json()
+    if not data or "pkg_name" not in data or "level" not in data:
+        return get_data_error_result(message="pkg_name and level are required")
+    pkg_name = data["pkg_name"]
+    level = data["level"]
+    success = set_log_level(pkg_name, level)
+    if success:
+        return get_json_result(data={"pkg_name": pkg_name, "level": level})
+    else:
+        return get_data_error_result(message=f"Invalid log level: {level}")