fix: invoice integrity — atomic numbering, safe delete, single create path

- Invoice numbers now come from DB function next_invoice_number()
  (max+1 per year under advisory lock) with a unique index; the old
  row-count method reused numbers after deletes and raced concurrent
  creates, which broke public pay links
- Remove dead standalone TeamCreateInvoice page; the TeamInvoices
  modal is the single create path (page had already drifted)
- Invoice delete now asks for confirmation and only un-bills tasks/
  submissions not billed on another invoice
- Created invoice shows correct "sent" status in list without reload
- Invoice/due dates computed at save time, not module load
- Reopening a paid invoice clears stale stripe_fee
- Stripe webhook markPaid is idempotent (no double receipts)
- subcontractor_invoice_items.version_number column stores billing
  version explicitly; description parsing kept as legacy fallback
- Drop unused buildInvoiceStatusByKey/deriveVersionStatus

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/SubcontractorInvoiceForm.jsx

@@ -120,7 +120,7 @@ export default function SubcontractorInvoiceForm({ embedded = false, onCancel, o
             .order('title'),
           supabase
             .from('subcontractor_invoices')
-            .select('id, status, items:subcontractor_invoice_items(task_id, description)')
+            .select('id, status, items:subcontractor_invoice_items(task_id, version_number, description)')
             .in('status', ['submitted', 'paid']),
           supabase.rpc('get_next_sub_invoice_number'),
         ]);
@@ -133,7 +133,9 @@ export default function SubcontractorInvoiceForm({ embedded = false, onCancel, o
         const invoicedUnitKeys = new Set(
           (existingInvoices || []).flatMap((inv) => asArray(inv.items).map((item) => {
             if (!item.task_id) return null;
-            return `${item.task_id}:${parseVersionFromDescription(item.description)}`;
+            // Stored version preferred; legacy rows (null) fall back to description parsing
+            const version = item.version_number != null ? Number(item.version_number) : parseVersionFromDescription(item.description);
+            return `${item.task_id}:${version}`;
           }).filter(Boolean))
         );
 
@@ -265,6 +267,7 @@ export default function SubcontractorInvoiceForm({ embedded = false, onCancel, o
         valid.map((item, idx) => ({
           invoice_id: inv.id,
           task_id: item.task_id || null,
+          version_number: item.task_id ? Number(item.version_number) || 0 : null,
           description: String(item.description).trim(),
           quantity: Number(item.quantity) || 1,
           unit_price: Number(item.unit_price) || 0,