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/generate_parent_chunks_gemma4.py

@@ -203,7 +203,7 @@ def main():
         )
 
     # Step 3: Generate summaries and insert
-    print(f"\n🤖 Generating summaries with gemma4...")
+    print("\n🤖 Generating summaries with gemma4...")
     inserted = insert_parent_chunks(scenes)
 
     print(f"\n{'=' * 70}")