feat: reset media form fields when modal is shown in MediaFormModal component

src/lib/MediaFormModal.svelte

@@ -12,7 +12,19 @@
     platform: '',
     notes: ''
   });
-
+  $effect(() => {
+    if (show) {
+      media = {
+        title: '',
+        type: '',
+        status: 'plan_to_watch',
+        date: '',
+        rating: 0,
+        platform: '',
+        notes: ''
+      };
+    }
+  });
   const statusOptions = [
     { value: 'plan_to_watch', label: '计划中' },
     { value: 'in_progress', label: '进行中' },