🟠 P1: Enable and validate pattern detection engine

[enioxt]

Problem

The pattern detection engine exists (10 risk detectors) but is disabled (PATTERNS_ENABLED=false). We claim to detect corruption patterns but we actually can't.

Detectors Available (need validation)

1. Contract splitting
2. Shell company detection
3. Single-source procurement
4. Unusual growth patterns
5. Cross-entity connections
6. And 5 more in api/src/bracc/routers/patterns.py

What We Need

• Test each detector against real Neo4j data
• Fix any that produce false positives
• Enable PATTERNS_ENABLED=true in production
• Document expected outputs for each pattern
• Add integration tests for pattern endpoints

Reference

docs/SYSTEM_CAPABILITIES_2026-03.md Section 11 — 'Where We LOSE'