meta: introduce Cypress end-to-end testing (via #4827)

* `test/e2e` -> `test/e2e-selenium`

* add Cypress

* ESLint fixes

* MOAR cypress

* `integration` -> `tests`

* wire Cypress up to a hot e2e server

* linter fixes

* don't run in CI

test/e2e-cypress/tests/.eslintrc

@@ -0,0 +1,8 @@
+globals:
+  cy: false
+  Cypress: false
+  expect: false
+  assert: false
+
+rules:
+  "no-console": 0

test/e2e-cypress/tests/deep-linking.js

@@ -0,0 +1,5 @@
+describe("The Home Page", function () {
+  it("successfully loads", function () {
+    cy.visit("/")
+  })
+})