Closes #1

❌ Problem

Running yarn start (or tsc --watch) threw

TS2550: Property 'includes' does not exist on type 'string[]'
because the project was compiled against the default ES5 lib set, which doesn’t contain Array.prototype.includes().

✅ Solution
• Bumped compilerOptions.target from ES5 → ES2017 in tsconfig.json.
• ES2017 brings in the lib definitions for Array#includes, Object.entries, async/await, etc.
• No runtime polyfills required because the example already targets modern browsers/Node ≥ 8.

🔬 Verification
• yarn build and yarn start now complete without type-errors.

📌 Notes
• Kept all other tsconfig options intact.
• No JavaScript output changes—only TypeScript typings.
• This is the minimal fix; if we ever need newer language features we can move to ES2020+.