refactor: media cards use proper <a href> links instead of JS navigation

MediaCard, MediaRow, CollageHero, HeroSection, and MediaDetail cast
cards now render as <a> tags with real hrefs. Modified clicks
(ctrl+click, middle-click) navigate natively, enabling open-in-new-tab
and link copying. Plain left-clicks continue through the existing
showDetail flow for side-effects like focus-state saving.

frontend/src/components/MediaRow.vue

@@ -10,13 +10,14 @@
       :item="item"
       :nav-row="rowIndex"
       :nav-col="index"
+      :href="getItemHref(item)"
       @click="$emit('select', item)"
     />
   </div>
 </template>
 
 <script setup lang="ts">
-import type { MediaItem } from "../types"
+import type { MediaItem, EpisodeWithSeries } from "../types"
 import MediaCard from "./MediaCard.vue"
 
 defineProps<{
@@ -28,4 +29,12 @@ defineProps<{
 defineEmits<{
   select: [MediaItem]
 }>()
+
+function getItemHref(item: MediaItem): string | undefined {
+  if (item.type === "episode") {
+    const epData = item.data as EpisodeWithSeries
+    return `#/series/${epData.series.id}`
+  }
+  return `#/${item.type}/${item.id}`
+}
 </script>