fix(demo-data): add version_family_id to data_contracts/data_products seeds

[larsgeorge-db]

Summary

Migration j1_add_version_family_id (PRD #442, commit 0ff3d77) made version_family_id NOT NULL on both data_contracts and data_products, but the demo SQL seeds in src/backend/src/data/demo_data_*.sql were never updated. Loading any vertical preset (retail, hls, auto, fsi, mfg) fails immediately:

psycopg2.errors.NotNullViolation: null value in column "version_family_id"
of relation "data_contracts" violates not-null constraint

Fix

Add version_family_id to the column list and set it to each row's own id in every INSERT INTO data_contracts / INSERT INTO data_products block. All seed rows are family roots (no parent), so version_family_id = id exactly matches the migration's recursive-CTE backfill semantics.

• 5 files patched (demo_data_retail, _hls, _auto, _fsi, _mfg)
• 10 INSERT blocks updated
• 27 contract rows + 27 product rows

Verified mechanically: every patched row's trailing version_family_id literal equals its leading id literal (0 mismatches).

Test plan

• Drop the local Postgres dev DB (or wipe the affected tables) and restart the backend; confirm startup_tasks loads demo data without NotNullViolation.
• Verify SELECT id, version_family_id FROM data_contracts; shows version_family_id = id for all seeded rows.
• Same check for data_products.
• Open the UI Data Contracts / Data Products lists and confirm the seeded demo entities render and the version-family selector works.