Add user database migration, core reusable components, and layout structure

web/lib/router.mjs

@@ -0,0 +1,33 @@
+class Router {
+  #routes = [];
+
+  on(pattern, handler) {
+    const regex = new RegExp(
+      '^' + pattern.replace(/:([^/]+)/g, '(?<$1>[^/]+)') + '$'
+    );
+    this.#routes.push({ regex, handler });
+    return this;
+  }
+
+  navigate(path) {
+    location.hash = '#' + path;
+  }
+
+  start() {
+    const dispatch = () => {
+      const path = decodeURIComponent(location.hash.slice(1)) || '/';
+      for (const { regex, handler } of this.#routes) {
+        const m = path.match(regex);
+        if (m) { handler(m.groups || {}); return; }
+      }
+    };
+    window.addEventListener('hashchange', dispatch);
+    dispatch();
+  }
+
+  get current() {
+    return decodeURIComponent(location.hash.slice(1)) || '/';
+  }
+}
+
+export const router = new Router();