fix(bulk-upload): handle network errors and partial upload success

save() now wraps each chunk fetch in try/catch — a thrown network error
marks all files in that chunk as errored. Also handles HTTP 200 responses
with a non-empty errors array (partial success): only the named filenames
are marked as errored rather than all files in the chunk. Navigation is
suppressed whenever any file fails.

Tests added:
- network error marks all chunk files as errored, no navigation
- HTTP 200 with errors array marks only affected files

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte

@@ -111,19 +111,29 @@ async function save() {
 		// Raw fetch is intentional: SvelteKit form actions can't stream chunked
 		// FormData with per-chunk progress. Session cookie is sent automatically
 		// by the browser for same-origin requests.
-		const res = await fetch('/api/documents/quick-upload', { method: 'POST', body: formData });
-		if (!res.ok) {
-			hadErrors = true;
+		try {
+			const res = await fetch('/api/documents/quick-upload', { method: 'POST', body: formData });
 			const body = await res.json().catch(() => ({ errors: [] }));
 			const errorFilenames = new Set<string>(
 				(body.errors ?? []).map((err: { filename: string }) => err.filename)
 			);
-			for (const entry of chunk) {
-				if (errorFilenames.has(entry.file.name)) {
-					const e = files.get(entry.id);
-					if (e) files.set(entry.id, { ...e, status: 'error' });
+			if (!res.ok || errorFilenames.size > 0) {
+				hadErrors = true;
+				for (const entry of chunk) {
+					// When backend names specific files, mark only those; otherwise mark all.
+					const isError = errorFilenames.size > 0 ? errorFilenames.has(entry.file.name) : true;
+					if (isError) {
+						const e = files.get(entry.id);
+						if (e) files.set(entry.id, { ...e, status: 'error' });
+					}
 				}
 			}
+		} catch {
+			hadErrors = true;
+			for (const entry of chunk) {
+				const e = files.get(entry.id);
+				if (e) files.set(entry.id, { ...e, status: 'error' });
+			}
 		}
 		chunkProgress = { done: i + 1, total: chunks.length };
 	}