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/search_blue_stamp.py

@@ -85,7 +85,7 @@ for frame_name in FRAMES:
                 cv2.rectangle(img, (x, y), (x + w, y + h), (0, 255, 0), 3)
                 cv2.putText(
                     img,
-                    f"BLUE STAMP?",
+                    "BLUE STAMP?",
                     (x, y - 10),
                     cv2.FONT_HERSHEY_SIMPLEX,
                     0.6,