`userId` and other ID columns are missing length caps; could allow oversized strings

[mercy60]

Internal ID: #86

Imported from ISSUES.md via scripts/import-issues.mjs.

Problem Statement. Repository inspection of entities is incomplete in scope, but userId strings in many schemas (matches, claims) lack length.

Expected Outcome.

• All ID columns capped at 64-128 chars.

Files / modules affected.

• All entities.

Dependencies. None.

Difficulty / Effort. Easy / S (≈ 2 hours).

Labels. area:backend, data-quality