fix: show download icon alongside file size in missing models dialog (#9850)

## Summary

Fix download icon not appearing when file size is successfully fetched
in the missing models dialog.

## Changes

- **What**: Restructured the `v-if/v-else-if` chain in
`MissingModelsContent.vue` so that file size and download icon render
together instead of being mutually exclusive. Previously, a successful
file size fetch would prevent the download button from rendering.

## Review Focus

The file size span and download/gated-link are now inside a shared
`<template v-else-if="model.isDownloadable">` block. File size uses
`v-if` (independent), while gated link and download button remain
`v-if/v-else` (mutually exclusive with each other).


[screen-capture.webm](https://github.com/user-attachments/assets/f2f04d52-265b-4d05-992e-0ffe9bf64026)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9850-fix-show-download-icon-alongside-file-size-in-missing-models-dialog-3226d73d365081fd943bcfdedda87c73)
by [Unito](https://www.unito.io)

src/components/dialog/content/MissingModelsContent.vue

@@ -30,31 +30,33 @@
           </div>
           <div class="flex shrink-0 items-center gap-2">
             <Skeleton v-if="showSkeleton(model)" class="ml-1.5 h-4 w-12" />
-            <span
-              v-else-if="model.isDownloadable && fileSizes.get(model.url)"
-              class="pl-1.5 text-xs text-muted-foreground"
-            >
-              {{ formatSize(fileSizes.get(model.url)) }}
-            </span>
-            <a
-              v-else-if="gatedModelUrls.has(model.url)"
-              :href="gatedModelUrls.get(model.url)"
-              target="_blank"
-              rel="noopener noreferrer"
-              class="text-xs text-primary hover:underline"
-            >
-              {{ $t('missingModelsDialog.acceptTerms') }}
-            </a>
-            <Button
-              v-else-if="model.isDownloadable"
-              variant="textonly"
-              size="icon"
-              :title="model.url"
-              :aria-label="$t('g.download')"
-              @click="downloadModel(model, paths)"
-            >
-              <i class="icon-[lucide--download] size-4" />
-            </Button>
+            <template v-else-if="model.isDownloadable">
+              <span
+                v-if="fileSizes.get(model.url)"
+                class="pl-1.5 text-xs text-muted-foreground"
+              >
+                {{ formatSize(fileSizes.get(model.url)) }}
+              </span>
+              <a
+                v-if="gatedModelUrls.has(model.url)"
+                :href="gatedModelUrls.get(model.url)"
+                target="_blank"
+                rel="noopener noreferrer"
+                class="text-xs text-primary hover:underline"
+              >
+                {{ $t('missingModelsDialog.acceptTerms') }}
+              </a>
+              <Button
+                v-else
+                variant="textonly"
+                size="icon"
+                :title="model.url"
+                :aria-label="$t('g.download')"
+                @click="downloadModel(model, paths)"
+              >
+                <i class="icon-[lucide--download] size-4" />
+              </Button>
+            </template>
             <Button
               v-else
               variant="textonly"