No foreign key validation during merge

[timsehn]

Problem

Merge operates on table hashes and row blobs without FK awareness. If Branch A deletes a parent row and Branch B adds a child row, the merge silently creates an FK violation.

Example

Ancestor: users(id=1), orders(user_id=1)
Branch A: DELETE FROM users WHERE id=1
Branch B: INSERT INTO orders VALUES(2, 1)
Merge: user 1 deleted + order referencing user 1 → FK violation

Expected behavior

• Load FK schema during merge
• Validate referential integrity post-merge
• Report FK violations as merge conflicts