UI refinements (#2859)

## Description:

UI Refinements requested by @evanpelle  check https://ui.openfront.dev

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced

## Please put your Discord username so you can be contacted if a bug or
regression is found:

w.o.n

src/client/Utils.ts

@@ -393,3 +393,29 @@ export async function getSvgAspectRatio(src: string): Promise<number | null> {
 
   return null;
 }
+
+export function getDiscordAvatarUrl(user: {
+  id: string;
+  avatar: string | null;
+  discriminator?: string;
+}): string | null {
+  if (user.avatar) {
+    // - id is a Discord numeric string
+    // - avatar is a hash, optionally prefixed with "a_" for animated avatars
+    const validId = /^\d+$/.test(user.id);
+    const validAvatar =
+      /^[a-f0-9]+$/.test(user.avatar) || /^a_[a-f0-9]+$/.test(user.avatar);
+
+    if (validId && validAvatar) {
+      const extension = user.avatar.startsWith("a_") ? "gif" : "png";
+      return `https://cdn.discordapp.com/avatars/${encodeURIComponent(user.id)}/${encodeURIComponent(user.avatar)}.${extension}?size=64`;
+    }
+  }
+
+  if (user.discriminator !== undefined) {
+    const idx = Number(user.discriminator) % 5;
+    return `https://cdn.discordapp.com/embed/avatars/${idx}.png`;
+  }
+
+  return null;
+}