Groom wizard steps 1-15: critique/harden/polish pass

- [P0] CrematoriumStep: Fix <option> → <MenuItem> in priority select
- [P1] All form steps: Add aria-busy={loading} + loading guard on submit
- [P1] Error messages: Replace color="error" (red) with copper
  (var(--fa-color-text-brand)) across ProvidersStep, PackagesStep,
  VenueStep, CrematoriumStep, CemeteryStep, CoffinsStep, PaymentStep
- [P2] IntroStep: "Has the person died?" → "Has this person passed away?"
- [P2] DateTimeStep: "About the person who died" → "who has passed"
- [P2] ProvidersStep: "Showing results from X" → "X providers found"
- [P2] Empty states: Add guidance text for ProvidersStep, PackagesStep,
  VenueStep, CoffinsStep empty results

Steps 4, 13, 15 passed with no issues.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/pages/PaymentStep/PaymentStep.tsx

@@ -161,9 +161,10 @@ export const PaymentStep: React.FC<PaymentStepProps> = ({
       <Box
         component="form"
         noValidate
+        aria-busy={loading}
         onSubmit={(e: React.FormEvent) => {
           e.preventDefault();
-          onConfirmPayment();
+          if (!loading) onConfirmPayment();
         }}
       >
         {/* ─── Payment plan ─── */}
@@ -229,7 +230,11 @@ export const PaymentStep: React.FC<PaymentStepProps> = ({
               </Paper>
             )}
             {errors?.card && (
-              <Typography variant="body2" color="error" sx={{ mt: 1 }} role="alert">
+              <Typography
+                variant="body2"
+                sx={{ mt: 1, color: 'var(--fa-color-text-brand)' }}
+                role="alert"
+              >
                 {errors.card}
               </Typography>
             )}
@@ -310,7 +315,11 @@ export const PaymentStep: React.FC<PaymentStepProps> = ({
           sx={{ mb: 1, alignItems: 'flex-start', '& .MuiCheckbox-root': { pt: 0.5 } }}
         />
         {errors?.termsAccepted && (
-          <Typography variant="body2" color="error" sx={{ mb: 2, ml: 4 }} role="alert">
+          <Typography
+            variant="body2"
+            sx={{ mb: 2, ml: 4, color: 'var(--fa-color-text-brand)' }}
+            role="alert"
+          >
             {errors.termsAccepted}
           </Typography>
         )}