refactor(cms): deduplicate shared admin components and fix studio batch completion

- fix(studio): stop markBatchDone infinite recursion so batches complete
- refactor(api): merge api-response into api and drop the duplicate module
- refactor(media): extract shared media loader and URL validator
- refactor(ui): extract shared LoadingSpinner for site and admin groups
- refactor(dates): consolidate raw date formatting into formatDate util
- refactor(logs): share a single generic log-list loader across tables
- refactor(theme): merge both ColorField components and reuse contrast helpers
- refactor(import): extract shared ImportErrorBanner and SearchInput
- chore(): remove dead theme-editor-tabs after inlining tab components

src/components/ui/loading-spinner.tsx

@@ -0,0 +1,25 @@
+type LoadingSpinnerProps = {
+	className?: string;
+	accentVar?: string;
+};
+
+/** Centered pulsing spinner used across site and admin loading.tsx placeholders. */
+export function LoadingSpinner({
+	className,
+	accentVar = "var(--color-primary)",
+}: LoadingSpinnerProps) {
+	return (
+		<div
+			style={{ display: "flex", justifyContent: "center", padding: "4rem 0" }}
+			className={className}
+		>
+			<div
+				className="animate-spin w-8 h-8 border-4 rounded-full"
+				style={{
+					borderColor: accentVar,
+					borderTopColor: "transparent",
+				}}
+			/>
+		</div>
+	);
+}