fix: refactor audit to SSE streaming, improve error handling

- Changed from blocking JSON endpoint to SSE streaming (like sync-all/repair-icons)
- Progress updates during each audit phase with item counts
- Proper error handling with typed AuditEvent for every failure path
- AbortController support for the client
- Shows real-time progress for each check section

src/app/api/admin/import/audit/route.ts

@@ -1,13 +1,46 @@
 import { withAdmin } from "@/lib/api-handler";
-import { apiError, apiOk } from "@/lib/api-response";
 import { PERMS } from "@/lib/permissions";
 import { runCatalogAudit } from "@/lib/services/catalog-audit";
 
+function sseEvent(data: unknown): string {
+	return `data: ${JSON.stringify(data)}\n\n`;
+}
+
 export const POST = withAdmin({ permission: PERMS.ASSETS_IMPORT }, async () => {
-	try {
-		const result = await runCatalogAudit();
-		return apiOk(result as unknown as Record<string, unknown>);
-	} catch (err) {
-		return apiError(`Audit failed: ${(err as Error).message}`, 500);
-	}
+	const encoder = new TextEncoder();
+
+	const stream = new ReadableStream({
+		async start(controller) {
+			const send = (data: unknown) => {
+				try {
+					controller.enqueue(encoder.encode(sseEvent(data)));
+				} catch {
+					/* stream closed */
+				}
+			};
+
+			try {
+				await runCatalogAudit(send);
+			} catch (err) {
+				send({
+					type: "error",
+					message: `Audit threw: ${(err as Error).message}`,
+				});
+			}
+
+			try {
+				controller.close();
+			} catch {
+				/* ignore */
+			}
+		},
+	});
+
+	return new Response(stream, {
+		headers: {
+			"Content-Type": "text/event-stream",
+			"Cache-Control": "no-cache",
+			Connection: "keep-alive",
+		},
+	});
 });