Move middlewares to dedicated folder with one per file

- Create src/middlewares/ folder with separate files:
  - os.ts: base implementer
  - auth.ts: authentication middleware
  - login-request.ts: login request middleware
  - superuser.ts: chains authMiddleware then checks superuser
- Update base.ts to re-export from middlewares
- Update admin procedures to use merged superuserMiddleware
  (no longer need to chain authMiddleware.use(superuserMiddleware))

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api-server/src/procedures/admin/users/list.ts

@@ -2,11 +2,10 @@
  * admin.users.list - List all users
  */
 
-import { authMiddleware, os, superuserMiddleware } from "../../base.js";
+import { os, superuserMiddleware } from "../../base.js";
 import { toUserResponse } from "../helpers.js";
 
 export const adminUsersList = os.admin.users.list
-  .use(authMiddleware)
   .use(superuserMiddleware)
   .handler(async ({ context }) => {
     const users = await context.db.selectFrom("users").selectAll().execute();