fix(content): update conditional checks to use mimeType for content rendering

- Replaced `type` field checks with `mimeType.startsWith("image/")` for improved accuracy in `content-card` and admin content page components.
- Adjusted `CardContent` background color for better visual consistency.

frontend/src/app/(dashboard)/admin/contents/page.tsx

@@ -98,7 +98,7 @@ export default function AdminContentsPage() {
 									<TableCell className="font-medium">
 										<div className="flex items-center gap-3">
 											<div className="flex h-10 w-10 items-center justify-center rounded bg-muted">
-												{content.type === "meme" ? (
+												{content.mimeType.startsWith("image/") ? (
 													<ImageIcon className="h-5 w-5 text-muted-foreground" />
 												) : (
 													<Video className="h-5 w-5 text-muted-foreground" />