data-studio-ui: add data-testid + E2E for documented flows (PH-DB-13)

G&A documentation audit (worker 6b1f3b26)

Lane: documentation / e2e cross-gap | PH: PH-DB-13

Finding

data-studio-ui documents project create, launch database, Database/SQL tabs but has:

• zero data-testid attributes
• no Playwright/Cypress tests
• npm run lint broken when NODE_ENV is non-standard

npm run build succeeds.

Coverage contract

Every documented user-facing flow needs test OR ga-gap issue (this issue).