ci: add cypress E2E workflow

[Jetshree]

Description

This PR adds a GitHub Actions workflow to automatically run Cypress E2E tests on every pull request and push to master.

The project already has Cypress configured with E2E tests in cypress/e2e/main.cy.js covering loading, audio controls, toolbar/navigation, file operations, UI elements, and Planet page interactions but there was no CI workflow to run them automatically. This PR closes that gap.

Triggers

• pull_request on opened and synchronize (every new commit on a PR)
• push to master branch

Steps

Step	Action	Details
Checkout	actions/checkout@v4	Checks out PR code
Setup Node	actions/setup-node@v4	Node 20 with npm caching
Run Cypress	cypress-io/github-action@v6	Installs deps (npm ci), starts server (npm start), waits for http://127.0.0.1:3000, runs all E2E tests in Chrome
Upload Screenshots	actions/upload-artifact@v4	Uploads cypress/screenshots as artifact on failure only

Security & Best Practices

• Uses pull_request (not pull_request_target) to ensure safe execution for external fork contributions
• No elevated permissions required, works with default read-only token
• Uses npm ci for reproducible installs from lockfile
• Uses npm caching (cache: 'npm') for faster CI runs
• Workflow fails automatically if Cypress exits with a non-zero status
• Screenshots uploaded as artifacts on failure for easy debugging

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[github-actions]

✅ All Jest tests passed! This PR is ready to merge.

[Jetshree]

@walterbender the e2e test was failing because fullscreen was not working properly in the CI environment, i have fixed that problem in this PR itself so that the checks pass and the PR can be merged cleanly.