Playwright e2e with DB-wipe fixture and test-DB guard

Serial e2e with the guard that makes wiping safe.

• e2e/*.e2e.ts, fullyParallel false, workers 1, global-setup migrates portfolio_test_e2e
• Fixture truncates via direct SQL before each test
• Guard refuses truncation unless NODE_ENV=test AND the database name ends _test or _test_e2e; the guard has its own unit test