Add EC2 deployment to CI/CD workflow

[khemssharma]

Adds a deploy-ec2 job to the existing CI/CD workflow so every push to main that passes the e2e job also deploys to the EC2 instance (i-0e7228c670843fdc7), in addition to the existing Render deploy.

What it does on the box (ubuntu@65.0.131.22, app cloned at ~/chess):

• Preserves ui/.env.production (hand-edited on the box to point at the EC2 IP instead of the Render URLs committed in the repo) across the reset
• • git fetch + reset --hard to origin/main
• • Rebuilds and recreates only the backend docker compose service (postgres/redis untouched)
• • Runs npm ci at the repo root on the host, then builds and rsyncs the ui/ frontend to /var/www/chess-frontend (nginx's docroot). The root install is required for ui's tsc build to resolve dotenv/@types/node while type-checking src/tests/runTests.ts.
    Before merging, add these repository secrets (Settings -> Secrets and variables -> Actions -> New repository secret):
• EC2_HOST = 65.0.131.22
• • EC2_USER = ubuntu
• • EC2_SSH_KEY = the private half of a dedicated ed25519 deploy key (generated on the box; its public half was appended to ~/.ssh/authorized_keys there, nothing else changed)
    I validated the build and frontend-deploy steps directly on the instance (docker image build, root+ui npm ci/build, rsync to /var/www/chess-frontend all succeeded); the actual docker compose up -d backend restart will happen on this workflow's first real run once the secrets are added.

[khemssharma]

ok fine. Let's try it