Secure Repository Queries + Injection Regression Guard

Goal: Remove any unsafe SQL query construction and add regression tests.
Rules:
1. Audit order_repository.py for string-built SQL.
2. If vulnerable patterns exist, replace with parameterized queries.
3. If already fixed, add/strengthen tests that prove malicious input does not change query semantics.
4. Keep behavior unchanged for valid input.
Definition of done:
1. Safe parameterized SQL in place.
2. Tests cover normal and malicious input.
3. Tests pass.