feat(platform-service): add P2 Product Intelligence modules (5 modules, 61 tests)
- experiments: A/B testing with FNV-1a deterministic variant assignment (7 endpoints, 15 tests)
- analytics: metric ingest + daily/weekly/monthly rollup queries (3 endpoints, 14 tests)
- feedback: in-app bug/feature/praise submission + admin triage (6 endpoints, 14 tests)
- impersonation: admin user impersonation with audit trail (4 endpoints, 6 tests)
- changelog: public product changelog with admin CRUD (6 endpoints, 12 tests)
- 6 new Cosmos containers added to cosmos-init.ts
- All 5 route modules registered in server.ts
- 1,090 total platform-service tests passing
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