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/face_processor_mps.py

@@ -18,7 +18,7 @@ import os
 import signal
 import time
 from datetime import datetime
-from typing import Dict, List, Optional, Tuple
+from typing import Dict, List
 
 import cv2
 import numpy as np
@@ -108,7 +108,7 @@ class MediaPipeFaceDetector:
                 print(f"[Face] Using fallback model: {alt_path}")
                 return alt_path
             
-            raise RuntimeError(f"Could not download MediaPipe model from any source")
+            raise RuntimeError("Could not download MediaPipe model from any source")
         
         return model_path