i18n(frontend): translate all German UI strings to English

Replace German labels, button text, toast messages, table headers,
tooltips, and placeholder strings across 7 files:
- WorkflowEditor: buttons, toasts, node labels
- Tenants: buttons, toasts, dialog text, table headers
- Admin: widget layout description
- OrderDetail: column headers (Baureihe→Series, Ebene→Level, Lagertyp→Bearing Type)
- ExcelSpreadsheet: column label definitions
- Upload: series/duplicate warning strings
- TemplateEditor: ALL_FIELD_DEFS default labels

API field names (baureihe, ebene1, produkt_baureihe etc.) unchanged.

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

frontend/src/pages/Upload.tsx

@@ -299,7 +299,7 @@ export default function UploadPage() {
 
             <p className="text-xs text-content-secondary mb-3 leading-relaxed">
               No products have been created yet. This is a <strong>preview</strong> of what will happen when you finalize the order.
-              Each unique <strong>Produkt (Baureihe)</strong> in the Excel becomes one product in the library.
+              Each unique <strong>Product (Series)</strong> in the Excel becomes one product in the library.
             </p>
 
             <div className="grid grid-cols-1 sm:grid-cols-2 lg:grid-cols-3 gap-3">
@@ -321,14 +321,14 @@ export default function UploadPage() {
                 icon={<Ban size={18} className="text-amber-600" />}
                 value={previewResult.no_pim_id_count}
                 label="rows skipped"
-                description="No PIM-ID or Baureihe found. Cannot be matched to a product."
+                description="No PIM-ID or Product Series found. Cannot be matched to a product."
                 color="bg-status-warning-bg border-border-default text-status-warning-text"
               />
               <StatCard
                 icon={<Copy size={18} className="text-orange-600" />}
                 value={previewResult.duplicate_count}
-                label="duplicate Baureihe"
-                description="Same Produkt-Baureihe appears multiple times. Pre-unchecked — only first occurrence imported."
+                label="duplicate Series"
+                description="Same Product Series appears multiple times. Pre-unchecked — only first occurrence imported."
                 color="bg-status-warning-bg border-border-default text-status-warning-text"
               />
             </div>
@@ -341,10 +341,10 @@ export default function UploadPage() {
                 <span className="text-status-warning-text font-bold text-sm shrink-0">⚠</span>
                 <div>
                   <p className="text-sm font-semibold text-status-warning-text">
-                    {previewResult.duplicate_count} duplicate Produkt-Baureihe row{previewResult.duplicate_count !== 1 ? 's' : ''} detected
+                    {previewResult.duplicate_count} duplicate Product Series row{previewResult.duplicate_count !== 1 ? 's' : ''} detected
                   </p>
                   <p className="text-xs text-status-warning-text mt-0.5">
-                    Each product is unique — only the <strong>first occurrence</strong> of a Baureihe will be imported.
+                    Each product is unique — only the <strong>first occurrence</strong> of a Product Series will be imported.
                     Duplicate rows are pre-unchecked (shown in amber). You can manually re-check them to overwrite the first.
                   </p>
                 </div>
@@ -378,7 +378,7 @@ export default function UploadPage() {
                     />
                   </th>
                   <th className="px-4 py-2 font-medium text-content-secondary">PIM-ID</th>
-                  <th className="px-4 py-2 font-medium text-content-secondary">Baureihe</th>
+                  <th className="px-4 py-2 font-medium text-content-secondary">Series</th>
                   <th className="px-4 py-2 font-medium text-content-secondary"
                     title="Gew\u00e4hltes Produkt \u2014 the specific material/coating variant from the Excel"
                   >Gew. Produkt</th>
@@ -424,14 +424,14 @@ export default function UploadPage() {
                         {!hasId ? (
                           <span
                             className="text-xs px-2 py-0.5 rounded-full bg-surface-muted text-content-muted"
-                            title="No PIM-ID or Baureihe — this row will be skipped"
+                            title="No PIM-ID or Product Series — this row will be skipped"
                           >
                             skipped
                           </span>
                         ) : row.is_duplicate ? (
                           <span
                             className="text-xs px-2 py-0.5 rounded-full bg-status-warning-bg text-status-warning-text font-medium"
-                            title={`Duplicate Produkt-Baureihe — first occurrence is row ${row.duplicate_of_row}. Uncheck to exclude.`}
+                            title={`Duplicate Product Series — first occurrence is row ${row.duplicate_of_row}. Uncheck to exclude.`}
                           >
                             Duplicate of row {row.duplicate_of_row}
                           </span>