feat(ui): align Dashboard Active and Recent Activity card heights

Both cards now use h-100 with a flex column layout so v-row stretches
them to match, and their v-card-text grows to fill so their footers
line up. Move Active's "+N more queued" out of the list body into a
proper v-card-actions footer mirroring Recent Activity's "View all
downloads" button.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/views/Dashboard.vue

@@ -140,7 +140,7 @@
     <v-row class="mt-4">
       <!-- Active Downloads (queued + running, auto-refresh) -->
       <v-col cols="12" md="4">
-        <v-card>
+        <v-card class="h-100 d-flex flex-column">
           <v-card-title class="d-flex align-center">
             <v-icon class="mr-2" :class="{ 'mdi-spin': activeDownloads.length }">
               {{ activeDownloads.length ? 'mdi-loading' : 'mdi-download' }}
@@ -160,7 +160,7 @@
               <v-icon>mdi-refresh</v-icon>
             </v-btn>
           </v-card-title>
-          <v-card-text>
+          <v-card-text class="flex-grow-1">
             <v-list v-if="activeDownloads.length" density="compact">
               <v-list-item
                 v-for="dl in visibleActiveDownloads"
@@ -181,11 +181,6 @@
                   </v-chip>
                 </v-list-item-subtitle>
               </v-list-item>
-              <v-list-item v-if="hiddenActiveCount" class="text-caption text-medium-emphasis">
-                <v-btn variant="text" size="small" to="/downloads?status=queued">
-                  +{{ hiddenActiveCount }} more queued
-                </v-btn>
-              </v-list-item>
             </v-list>
             <div v-else class="text-center py-8">
               <v-icon size="48" color="secondary" :style="{ opacity: 0.5 }">mdi-check-circle-outline</v-icon>
@@ -193,19 +188,24 @@
               <div class="text-caption text-medium-emphasis mt-1">All sources are idle</div>
             </div>
           </v-card-text>
+          <v-card-actions>
+            <v-btn variant="text" :to="hiddenActiveCount ? '/downloads?status=queued' : '/downloads'">
+              {{ hiddenActiveCount ? `View all downloads (+${hiddenActiveCount} more queued)` : 'View all downloads' }}
+            </v-btn>
+          </v-card-actions>
         </v-card>
       </v-col>
 
       <!-- Recent Activity -->
       <v-col cols="12" md="8">
-        <v-card>
+        <v-card class="h-100 d-flex flex-column">
           <v-card-title>
             Recent Activity
             <v-chip v-if="recentActivity.length" size="small" class="ml-2" variant="tonal">
               Last 7 days
             </v-chip>
           </v-card-title>
-          <v-card-text>
+          <v-card-text class="flex-grow-1">
             <v-list v-if="recentActivityGrouped.length">
               <template v-for="entry in visibleRecentActivity" :key="entry.key">
                 <v-list-item v-if="entry.kind === 'single'">