chore: pre-existing in-tree work (event-study/research/vintages/prices + migration script + integrity docs)

Committing the prior uncommitted working-tree state that predates this session's
data-source work (was already modified/untracked at session start) so the tree
is clean before push. Includes: event-study + research report integrity/forward
observation work, prices tests, research hash migration script, and the
2026-08-23/24 engineering-log + test-evidence notes. Verified green as part of
the full 362-test suite.

backend/scripts/migrate_research_report_hashes.py

@@ -0,0 +1,27 @@
+"""Migrate legacy research reports into the fail-closed hashed format."""
+
+from __future__ import annotations
+
+import argparse
+import json
+from pathlib import Path
+
+from app.research import ResearchRunStore
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument(
+        "--root",
+        type=Path,
+        default=Path(__file__).resolve().parents[1] / "data" / "research",
+        help="research store root containing manifest.json and reports/",
+    )
+    args = parser.parse_args()
+    migrated = ResearchRunStore(args.root).migrate_legacy()
+    print(json.dumps({"migrated_reports": migrated}, sort_keys=True))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())