Bust avatar/banner cache so new image shows on all pages

After my previous fix the upload succeeds, but the avatar path is always
.../profile/avatar.<ext>, so its media URL never changes. Pages other than the
channel (which cache-busts with ?t=) kept serving the browser-cached OLD image
— the user "still saw the old avatar" on /videos.

- avatar_url / banner_url accessors append ?v=<updated_at timestamp>.
- updateAvatar / updateBanner now bump updated_at explicitly (the path is
  unchanged, so Eloquent wouldn't otherwise touch it), changing ?v so every
  page fetches the new image.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

app/Models/User.php

@@ -162,7 +162,10 @@ class User extends Authenticatable implements MustVerifyEmail
     public function getAvatarUrlAttribute(): string
     {
         if ($this->avatar) {
-            return route('media.avatar', $this->avatar);
+            // ?v busts the browser cache when the avatar is replaced. The path is
+            // always .../profile/avatar.<ext>, so without a version every page would
+            // keep showing the previously cached image after an upload.
+            return route('media.avatar', $this->avatar).'?v='.($this->updated_at?->timestamp ?? '0');
         }
 
         return 'https://i.pravatar.cc/150?u='.$this->id;
@@ -171,7 +174,7 @@ class User extends Authenticatable implements MustVerifyEmail
     public function getBannerUrlAttribute(): ?string
     {
         if ($this->banner) {
-            return route('media.banner', $this->banner);
+            return route('media.banner', $this->banner).'?v='.($this->updated_at?->timestamp ?? '0');
         }
         return null;
     }