Code with no tests is code nobody wants to touch. Pick one module, service or set of API routes, and I'll add tests that cover how it really behaves: the normal cases, the edge cases and the error paths. I use the test setup you already have (Vitest, Jest, Playwright or pytest), or add a lightweight one if there is none. Any bugs the tests uncover are reported to you, not silently changed. You get a pull request with the new tests passing in your CI, a short summary of what is now covered and what isn't, and notes on any risky code worth a closer look.