feat: persistent multi-step undo system in TopBar

fix: save all changes to Supabase with reliable upsert

- Replace broken PATCH→POST fallback with single atomic upsert (POST +
  Prefer: resolution=merge-duplicates). The old PATCH returned 200 OK
  with empty body for new articles, causing silent data loss on every
  first save per article.
- Fix getAllSyncedRows pagination: add explicit limit=10000 and Range
  header to bypass Supabase's default 1000-row cap.
- Add fetchWithRetry helper (2 retries on 5xx/network errors).
- handleSaveRow now returns Promise<boolean> and closes EditPanel only
  after a confirmed successful save.
- Add 'error' save status: failed rows turn red (border-l-red-500)
  across ProductDescriptions, ArticleDetails, and PricingView.
- EditPanel shows saving spinner, disables buttons while saving, and
  displays inline error message with "Retry Save" on failure.

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

src/components/PricingView.tsx

@@ -455,19 +455,21 @@ export function PricingView({ data, headers, onSaveRow, onCaptureState, onEdit,
             <tbody>
               {filteredRows.map(({ row, dataIndex, pricingErrors, unitErrors, isCritical }) => {
                 const hasAnyError = pricingErrors.length > 0 || unitErrors.length > 0;
-                const isPending = rowStatuses[String(row[COLUMNS.ARTICLE_NO])] === 'pending';
+                const saveStatus = rowStatuses[String(row[COLUMNS.ARTICLE_NO])];
                 return (
                   <tr
                     key={dataIndex}
                     className={cn(
                       'border-b border-slate-700/50 transition-colors hover:bg-slate-700/20',
-                      isPending 
-                        ? 'bg-yellow-400/20 border-l-4 border-l-yellow-400' 
-                        : isCritical
-                          ? 'bg-red-950/20'
-                          : pricingErrors.length > 0
-                            ? 'bg-amber-950/10'
-                            : ''
+                      saveStatus === 'error'
+                        ? 'bg-red-400/20 border-l-4 border-l-red-500'
+                        : saveStatus === 'pending'
+                          ? 'bg-yellow-400/20 border-l-4 border-l-yellow-400'
+                          : isCritical
+                            ? 'bg-red-950/20'
+                            : pricingErrors.length > 0
+                              ? 'bg-amber-950/10'
+                              : ''
                     )}
                   >
                     {/* Article No */}