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/CemeteryStep/CemeteryStep.tsx

@@ -159,9 +159,10 @@ export const CemeteryStep: React.FC<CemeteryStepProps> = ({
       <Box
         component="form"
         noValidate
+        aria-busy={loading}
         onSubmit={(e: React.FormEvent) => {
           e.preventDefault();
-          onContinue();
+          if (!loading) onContinue();
         }}
       >
         {/* ─── Burial plot question ─── */}
@@ -177,7 +178,11 @@ export const CemeteryStep: React.FC<CemeteryStepProps> = ({
             <FormControlLabel value="no" control={<Radio />} label="No, we need to find one" />
           </RadioGroup>
           {errors?.burialOwn && (
-            <Typography variant="body2" color="error" sx={{ mt: 0.5 }} role="alert">
+            <Typography
+              variant="body2"
+              sx={{ mt: 0.5, color: 'var(--fa-color-text-brand)' }}
+              role="alert"
+            >
               {errors.burialOwn}
             </Typography>
           )}
@@ -201,7 +206,11 @@ export const CemeteryStep: React.FC<CemeteryStepProps> = ({
               />
             </RadioGroup>
             {errors?.burialCustom && (
-              <Typography variant="body2" color="error" sx={{ mt: 0.5 }} role="alert">
+              <Typography
+                variant="body2"
+                sx={{ mt: 0.5, color: 'var(--fa-color-text-brand)' }}
+                role="alert"
+              >
                 {errors.burialCustom}
               </Typography>
             )}
@@ -257,7 +266,11 @@ export const CemeteryStep: React.FC<CemeteryStepProps> = ({
             </Box>
 
             {errors?.selectedCemeteryId && (
-              <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.selectedCemeteryId}
               </Typography>
             )}