Fix Back button on SignIn page & Add Cancel button (#6415)

* Back button on SignIn page leads to Home page
Fixes #6413

* Add regression test for the bug, and for new cancel button

* Full sign in e2e test

* Good bot

Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>

---------

Co-authored-by: graphite-app[bot] <96075541+graphite-app[bot]@users.noreply.github.com>

e2e/playwright/auth.spec.ts

@@ -0,0 +1,53 @@
+import { expect, test } from '@e2e/playwright/zoo-test'
+
+// test file is for testing auth functionality
+test.describe('Authentication tests', () => {
+  test(
+    `The user can sign out and back in`,
+    { tag: ['@electron'] },
+    async ({ page, homePage, signInPage, toolbar, tronApp }) => {
+      if (!tronApp) {
+        fail()
+      }
+
+      await page.setBodyDimensions({ width: 1000, height: 500 })
+      await homePage.projectSection.waitFor()
+
+      await test.step('Click on sign out and expect sign in page', async () => {
+        await toolbar.userSidebarButton.click()
+        await toolbar.signOutButton.click()
+        await expect(signInPage.signInButton).toBeVisible()
+      })
+
+      await test.step('Click on sign in and cancel, click again and expect different code', async () => {
+        await signInPage.signInButton.click()
+        await expect(signInPage.userCode).toBeVisible()
+        const firstUserCode = await signInPage.userCode.textContent()
+        await signInPage.cancelSignInButton.click()
+        await expect(signInPage.signInButton).toBeVisible()
+
+        await signInPage.signInButton.click()
+        await expect(signInPage.userCode).toBeVisible()
+        const secondUserCode = await signInPage.userCode.textContent()
+        expect(secondUserCode).not.toEqual(firstUserCode)
+      })
+
+      await test.step('Press back button and remain on home page', async () => {
+        await page.goBack()
+        await expect(homePage.projectSection).not.toBeVisible()
+        await expect(signInPage.signInButton).toBeVisible()
+      })
+
+      await test.step('Sign in, activate, and expect home page', async () => {
+        await signInPage.signInButton.click()
+        await expect(signInPage.userCode).toBeVisible()
+        const userCode = await signInPage.userCode.textContent()
+        expect(userCode).not.toBeNull()
+        await signInPage.verifyAndConfirmAuth(userCode!)
+
+        // Longer timeout than usual here for the wait on home page
+        await expect(homePage.projectSection).toBeVisible({ timeout: 10000 })
+      })
+    }
+  )
+})