Add a database-backed environment for testing

[willdaly]

Summary

The project spec explicitly says the MVP is local-only and has no database. The whiteboard calls out building a database for testing so the team can validate the product with more realistic flows.

Scope

• choose a lightweight persistence option for hackathon use
• store profiles and match history outside localStorage
• make it easy to reset and reseed test data

Acceptance criteria

• test profiles and matches persist outside the browser session
• the team can run repeatable testing against shared data
• local-only storage is no longer the only persistence path