Enhance user profile management and Gravatar integration

- Added email field to user profile API and frontend components for better user identification.
- Implemented PATCH /map/api/me endpoint to update user email, enhancing user experience.
- Introduced useGravatarUrl composable for generating Gravatar URLs based on user email.
- Updated profile and layout components to display user avatars using Gravatar, improving visual consistency.
- Enhanced development documentation to guide testing of navbar and profile features.

frontend-nuxt/composables/useGravatarUrl.ts

@@ -0,0 +1,16 @@
+import md5 from 'md5'
+
+/**
+ * Returns Gravatar avatar URL for the given email, or empty string if no email.
+ * Gravatar expects: trim, lowercase, then MD5 hex. Use empty string to show a placeholder (e.g. initial letter) in the UI.
+ *
+ * @param email - User email (optional)
+ * @param size - Avatar size in pixels (default 64; navbar 32, drawer 40, profile 64–80)
+ */
+export function useGravatarUrl(email: string | undefined, size?: number): string {
+  const normalized = email?.trim().toLowerCase()
+  if (!normalized) return ''
+  const hash = md5(normalized)
+  const s = size ?? 64
+  return `https://www.gravatar.com/avatar/${hash}?s=${s}&d=identicon`
+}