chore: add ci

[devrodri-com]

What changed

• Adds a minimal GitHub Actions CI workflow for pull requests and pushes to main.
• Uses Node.js 20 with npm cache and npm ci.
• Runs a conservative TypeScript no-emit build check over deployable api/**/*.ts files.
• Runs the existing Vercel Serverless Function count guardrail.

What is intentionally omitted

• No lint step because package.json has no lint script.
• No test step because package.json has no test script.
• No production deploy, Vercel command, secrets, or environment variables are used.
• No application logic changed.

Validation

• npm ci
• find api -name '*.ts' -print0 | xargs -0 npm exec tsc -- --noEmit --skipLibCheck --moduleResolution node --target ES2022 --module commonjs --esModuleInterop
• npm run check:vercel-functions
• Parsed .github/workflows/ci.yml with Ruby YAML.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
mutter-games-admin-api	Ready	Preview, Comment	May 12, 2026 1:35pm
mutter-games-admin-api-prod	Ready	Preview, Comment	May 12, 2026 1:35pm