feat: replace native date inputs with shadcn date picker

Add calendar + popover components and a custom DateTimePicker wrapper.
Video forms use date-only; article forms include a time picker.
Also add video player preview to the video edit form.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/admin/videos/[id]/+page.svelte

@@ -11,6 +11,7 @@
   import { FileDropZone, MEGABYTE } from "$lib/components/ui/file-drop-zone";
   import { getAssetUrl } from "$lib/api";
   import { Select, SelectContent, SelectItem, SelectTrigger } from "$lib/components/ui/select";
+  import { DatePicker } from "$lib/components/ui/date-picker";
 
   const { data } = $props();
 
@@ -124,7 +125,12 @@
     <div class="space-y-1.5">
       <Label>{$_("admin.video_form.video_file")}</Label>
       {#if movieId}
-        <p class="text-xs text-muted-foreground mb-1">{$_("admin.video_form.current_file", { values: { id: movieId } })}</p>
+        <video
+          src={getAssetUrl(movieId)}
+          poster={imageId ? getAssetUrl(imageId, "preview") ?? undefined : undefined}
+          controls
+          class="w-full rounded-lg bg-black max-h-72 mb-2"
+        ></video>
       {/if}
       <FileDropZone accept="video/*" maxFileSize={2000 * MEGABYTE} onUpload={handleVideoUpload} />
     </div>
@@ -135,8 +141,8 @@
     </div>
 
     <div class="space-y-1.5">
-      <Label for="uploadDate">{$_("admin.common.publish_date")}</Label>
-      <Input id="uploadDate" type="datetime-local" bind:value={uploadDate} />
+      <Label>{$_("admin.common.publish_date")}</Label>
+      <DatePicker bind:value={uploadDate} placeholder={$_("admin.common.publish_date")} showTime={false} />
     </div>
 
     <div class="flex gap-6">