Add image cropping to avatar upload and show avatars platform-wide

- Add react-easy-crop for circular crop + zoom UI on avatar upload
- Create server-side getUserAvatarUrl utility for generating pre-signed URLs
- Update all nav components (admin, jury, mentor, observer) to show user avatars
- Add avatar URLs to user list, mentor list, and project detail API responses
- Replace initials-only avatars with UserAvatar component across admin pages

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

src/server/utils/avatar-url.ts

@@ -0,0 +1,35 @@
+import { createStorageProvider, type StorageProviderType } from '@/lib/storage'
+
+/**
+ * Generate a pre-signed download URL for a user's avatar.
+ * Returns null if the user has no avatar.
+ */
+export async function getUserAvatarUrl(
+  profileImageKey: string | null | undefined,
+  profileImageProvider: string | null | undefined
+): Promise<string | null> {
+  if (!profileImageKey) return null
+
+  try {
+    const providerType = (profileImageProvider as StorageProviderType) || 's3'
+    const provider = createStorageProvider(providerType)
+    return await provider.getDownloadUrl(profileImageKey)
+  } catch {
+    return null
+  }
+}
+
+/**
+ * Batch-generate avatar URLs for multiple users.
+ * Adds `avatarUrl` field to each user object.
+ */
+export async function attachAvatarUrls<
+  T extends { profileImageKey?: string | null; profileImageProvider?: string | null }
+>(users: T[]): Promise<(T & { avatarUrl: string | null })[]> {
+  return Promise.all(
+    users.map(async (user) => ({
+      ...user,
+      avatarUrl: await getUserAvatarUrl(user.profileImageKey, user.profileImageProvider),
+    }))
+  )
+}