Add username/password auth and login UI

wwwroot/js/api.js

@@ -24,7 +24,9 @@ async function request(path, { method = "GET", body, adminKey } = {}) {
       const data = await res.json();
       msg = data.error || JSON.stringify(data);
     } catch { /* ignore */ }
-    throw new Error(msg);
+    const err = new Error(msg);
+    err.status = res.status;
+    throw err;
   }
   return res.status === 204 ? null : res.json();
 }
@@ -33,6 +35,9 @@ export const api = {
   state: () => request("/api/state"),
   me: () => request("/api/me"),
   setName: (name) => request("/api/me/name", { method: "POST", body: { name } }),
+  register: (payload) => request("/api/auth/register", { method: "POST", body: payload }),
+  login: (payload) => request("/api/auth/login", { method: "POST", body: payload }),
+  logout: () => request("/api/auth/logout", { method: "POST" }),
 
   mySuggestions: () => request("/api/suggestions/mine"),
   createSuggestion: (payload) => request("/api/suggestions", { method: "POST", body: payload }),