Add Playwright happy-path E2E

[ejones23]

Summary

• add Playwright config and scripts for a create -> vote -> results happy-path E2E
• create and tear down an isolated MySQL rcv_e2e database for browser tests
• add inert data-testid hooks to the AngularJS templates for stable E2E selectors
• harden the harness for future CI use with run-specific DB names, ports, and cache directories
• scope the test to active views/forms and assert against dedicated candidate-name and winner elements to reduce flake risk

Verification

• npm run test:e2e
• npm test
• npm run build
• ran the Playwright happy-path 10 times in two concurrent batches of 5; all 10 passed

[DavidMeritas]

Great work on this, ejones! Really well thought out — the run isolation with per-run DB names, ports, and cache dirs is exactly the kind of thing that saves headaches down the road in CI. The data-testid approach for selectors is solid, the SQL injection guards are a nice touch, and the whole create → vote → results happy path reads cleanly. Love the E2E_KEEP_DB=1 escape hatch for debugging too. Thanks for continuing to level up the test infrastructure — this project is in much better shape because of your contributions. 🎉