feat: Phase 2.6 edges migration to Qdrant (TKG-only architecture)

Phase 2.6.1: co_occurrence_edges migration
- build_co_occurrence_edges_from_qdrant()
- Qdrant embeddings → frame grouping → YOLO objects
- Result: 6679 edges (vs 6701 PostgreSQL)

Phase 2.6.2: face_face_edges migration
- build_face_face_edges_from_qdrant()
- Qdrant embeddings → frame grouping → face pairs
- mutual_gaze detection preserved
- Result: 6 edges (exact match)

Phase 2.6.3: speaker_face_edges migration
- build_speaker_face_edges_from_qdrant()
- Qdrant embeddings → trace_id frame ranges
- SPEAKS_AS edge creation

Architecture:
- All edges use Qdrant payload (no face_detections queries)
- PostgreSQL fallback for empty Qdrant
- Estimated 3.6x performance improvement

Testing:
- Playground (3003): ✓ All Phase 2.6 logs verified
- Edge counts: ✓ Close match with PostgreSQL
- Fallback: ✓ Working

Docs:
- docs_v1.0/DESIGN/TKG_PHASE2_6_EDGES_MIGRATION.md
- docs_v1.0/M4_workspace/2026-06-21_phase2_6_test.md

scripts/backfill_face_id.py

@@ -0,0 +1,76 @@
+#!/opt/homebrew/bin/python3.11
+"""Backfill face_id for existing face_detections rows using trace_id.
+
+face_id is generated as 'face_{trace_id}' for each unique trace.
+This covers past data where face_id was never written.
+"""
+
+import os
+import psycopg2
+
+DB_URL = os.environ.get("DATABASE_URL", "postgresql://accusys@localhost:5432/momentry")
+SCHEMA = os.environ.get("MOMENTRY_DB_SCHEMA", "dev")
+
+
+def get_conn():
+    return psycopg2.connect(DB_URL)
+
+
+def backfill_by_trace(file_uuid: str, schema: str = SCHEMA) -> int:
+    """Set face_id = 'face_{trace_id}' for all rows with NULL face_id and non-NULL trace_id."""
+    conn = get_conn()
+    cur = conn.cursor()
+
+    cur.execute(
+        f"""
+        UPDATE {schema}.face_detections
+        SET face_id = 'face_' || trace_id::text
+        WHERE file_uuid = %s
+          AND face_id IS NULL
+          AND trace_id IS NOT NULL
+        """,
+        (file_uuid,),
+    )
+    updated = cur.rowcount
+    conn.commit()
+    cur.close()
+    conn.close()
+    return updated
+
+
+def main():
+    conn = get_conn()
+    cur = conn.cursor()
+
+    # Count rows that need backfill
+    cur.execute(
+        f"""SELECT COUNT(*) FROM {SCHEMA}.face_detections
+            WHERE face_id IS NULL AND trace_id IS NOT NULL"""
+    )
+    total_rows = cur.fetchone()[0]
+
+    cur.execute(
+        f"""SELECT DISTINCT file_uuid FROM {SCHEMA}.face_detections
+            WHERE face_id IS NULL AND trace_id IS NOT NULL"""
+    )
+    uuids = [row[0] for row in cur.fetchall()]
+    cur.close()
+    conn.close()
+
+    if not uuids:
+        print("No rows need backfill (all face_id already set or no trace_id).")
+        return
+
+    print(f"Found {total_rows} rows across {len(uuids)} files to backfill")
+
+    total_all = 0
+    for uuid in uuids:
+        count = backfill_by_trace(uuid)
+        total_all += count
+        print(f"  [{uuid}] updated {count} rows")
+
+    print(f"\nDone: {len(uuids)} files, {total_all} rows updated")
+
+
+if __name__ == "__main__":
+    main()