feat(ui): unify VAT rate+toggle layout (offers/invoices/orders); move offers secondary row actions into an overflow menu

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/InvoiceDetail.tsx

@@ -1889,7 +1889,7 @@ export default function InvoiceDetail() {
           <Box
             sx={{
               display: "grid",
-              gridTemplateColumns: { xs: "1fr", md: "1fr 1fr 1fr 1fr" },
+              gridTemplateColumns: { xs: "1fr", md: "repeat(5, 1fr)" },
               gap: 2,
             }}
           >
@@ -1934,6 +1934,23 @@ export default function InvoiceDetail() {
                 ]}
               />
             </Field>
+            {/* Document-default VAT rate. Presentational only — it writes the
+                already-existing `form.vat_rate` (used to seed new line rows /
+                as the per-line fallback). Totals are computed per-line from
+                `item.vat_rate`, so changing this does NOT alter computed VAT. */}
+            <Field label="Sazba DPH">
+              <Select
+                value={String(form.vat_rate)}
+                disabled={!form.apply_vat}
+                onChange={(val) =>
+                  setForm((prev) => ({ ...prev, vat_rate: Number(val) }))
+                }
+                options={vatOptions.map((o) => ({
+                  value: String(o.value),
+                  label: o.label,
+                }))}
+              />
+            </Field>
             <Field label="DPH">
               <Box sx={{ display: "flex", alignItems: "center", height: 40 }}>
                 <CheckboxField