fix(e2e): complete Cypress migration and stabilize make e2e for #523

[PRAteek-singHWY]

Fixes #523

Summary

This PR completes the E2E migration path to Cypress and restores a working smoke test flow.

What changed

• switched test:e2e from jest to cypress run in package.json
• added Cypress scripts:
  • cypress:open
  • cypress:run
• added root Cypress config: cypress.config.js
• added smoke suite: cypress/e2e/smoke.cy.js
• removed obsolete legacy files:
  • cypress.json
  • application/frontend/src/test/basic-e2e.test.ts (commented Jest/Puppeteer test)
• fixed make e2e in Makefile:
  • deterministic Flask startup on 127.0.0.1:5000
  • readiness wait loop before test run
  • process cleanup via trap
  • env -u ELECTRON_RUN_AS_NODE yarn test:e2e for stable Cypress execution
• removed obsolete playwright install step from install-python (Makefile), consistent with Cypress migration

Validation

• ran: make e2e
• result: Cypress smoke suite passed
• outcome: 3 passing, 0 failing

Scope notes

• this PR is intentionally scoped to fix e2e tests #523 (restore/fix e2e with Cypress)
• no unrelated frontend build artifacts are included

[PRAteek-singHWY]

Hi @northdpole picked this up based on your earlier guidance to finish the Cypress migration for e2e.

PR #774 incorporates the prior review iterations from related e2e threads (#729, #732) and is scoped to resolve #523:

• test:e2e switched to Cypress
• make e2e stabilized (Flask startup, readiness wait, cleanup trap)
• smoke coverage for home/search/browse routes
• obsolete legacy e2e files/config removed

Validation: make e2e passes locally (3 passing).