Fix log file name in API logging tests

Update robot tests to use correct log file name 'fastapi_app.log'
instead of 'aniworld.log'. Also remove completed Task 4 documentation
from tasks.md.

Docs/tasks.md

@@ -1,18 +1,3 @@
-## Task 4: API Logging - Get Logging Config
-
-**Suite:** `Robot.Api.Logging`  
-**Test:** `Get Logging Config`  
-**Result:** FAIL  
-**Error:** `Dictionary does not contain key 'level'.`
-
-**Instructions:**
-- Investigate the `GET /api/logging/config` endpoint response.
-- The test expects a `level` key in the logging config JSON, but it is missing.
-- Check the logging config model/response in the backend and ensure `level` is included.
-- If the field was renamed (e.g., to `log_level`), update the test in `tests/robot/api/logging.robot` accordingly.
-
----
-
 ## Task 5: API Logging - Tail Log File
 
 **Suite:** `Robot.Api.Logging`