Add End-to-End Testing to HydroServer CI

[daniel-slaugh]

Currently, HydroServer is only tested with unit tests and Standardized Testing document someone has to walk through manually.

Add Playwright e2e tests to automate some of the manual testing. Organize and document the approach so a someone can clearly see:

1. What's covered by unit tests
2. What's covered by e2e tests
3. What needs to be manually checked each release