feat: Implement username change functionality

src/lib/validation.ts

@@ -0,0 +1,17 @@
+import { z } from 'zod';
+
+export const usernameSchema = z
+  .string()
+  .min(3, 'Username must be at least 3 characters')
+  .max(30, 'Username must be less than 30 characters')
+  .regex(/^[a-zA-Z0-9_-]+$/, 'Username can only contain letters, numbers, underscores, and hyphens')
+  .regex(/^[a-zA-Z0-9]/, 'Username must start with a letter or number')
+  .transform(val => val.toLowerCase());
+
+export const profileEditSchema = z.object({
+  username: usernameSchema,
+  display_name: z.string().max(100, 'Display name must be less than 100 characters').optional(),
+  bio: z.string().max(500, 'Bio must be less than 500 characters').optional(),
+});
+
+export type ProfileEditForm = z.infer<typeof profileEditSchema>;