Browser end-to-end (e2e) tests for the session builder and tools #255

Is your feature request related to a problem? Please describe. The repo has Vitest unit tests but nothing that checks the UI in a browser, so a break in the 3-step session builder or the tool calculators
would only be caught by hand.

Describe the solution you'd like A small set of browser end-to-end tests under e2e/kane/: stepping through the session builder (equipment → muscles → exercises) and checking the BMI calculator's result. No
app code changes; ESLint would skip the folder.

Describe alternatives you've considered Plain Playwright specs. These are written as plain-English _test.md files with KaneCLI, and each also has an exported Playwright (JavaScript) version.

Additional context While setting up locally I noticed make setup fails on a fresh database: prisma/migrations only has 0_init, which doesn't create columns that schema.prisma now has (e.g.
user.onboardingPreferences), so db:seed-leaderboard crashes with P2022. prisma db push works around it. Disclosure: I work at TestMu AI, which makes KaneCLI. Happy to open a PR if this sounds useful.