Stage 2: The Router

Every framework's app.get("/users/:id", handler) is a tiny pattern matcher. Build it.

Implement createRouter() returning:

• add(method, pattern, handler) — register a route; pattern segments starting with : are parameters (/users/:id/posts/:postId)
• handle(method, path) — find the matching route and return handler({ params }); return { status: 404 } if no pattern matches, and { status: 405 } if a pattern matches but with the wrong method (real servers distinguish "no such resource" from "wrong verb").

Matching rules: exact segment count, literal segments must equal, : segments capture. First registered match wins.