cleanup: remove dead code and duplicate docs

- Remove session-ses_2f27.md (161KB raw session log)
- Remove 49 ROOT_* duplicate files across REFERENCE/
- Remove 14 duplicate files between REFERENCE/ root and history/
- Remove asr_legacy.rs (dead code, replaced by asr.rs)
- Remove src/core/worker/ (duplicate JobWorker)
- Remove src/core/layers/ (empty directory)
- Remove 4 .bak files in src/
- Remove 7 dead private methods in worker/processor.rs
- Remove backup directory from git tracking

scripts/test_speechbrain.py

@@ -5,9 +5,7 @@ SpeechBrain 測試腳本
 """
 
 import sys
-import json
 import time
-from pathlib import Path
 
 def test_asr(video_path):
     """測試 SpeechBrain ASR"""