Fix multi-click submit bug and add draft submit indicator on juror dashboard

- Initialize slider values to midpoint so visual matches stored value
  (root cause: sliders appeared filled but criteriaValues was undefined)
- Use mutateAsync for submit to properly await and prevent double-clicks
- Add startMutation.isPending to submit button disabled state
- Add error toast in evaluation-form.tsx catch block (was silent)
- Show "Ready to submit" badge and "Review & Submit" button for drafts
  on juror dashboard

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

src/components/forms/evaluation-form.tsx

@@ -303,7 +303,10 @@ export function EvaluationForm({
 
   // Submit handler
   const onSubmit = async (data: EvaluationFormData) => {
-    if (!currentEvaluationId) return
+    if (!currentEvaluationId) {
+      toast.error('Evaluation is still being created. Please wait a moment and try again.')
+      return
+    }
 
     try {
       await submit.mutateAsync({
@@ -325,6 +328,7 @@ export function EvaluationForm({
       })
     } catch (error) {
       console.error('Submit failed:', error)
+      toast.error(error instanceof Error ? error.message : 'Failed to submit evaluation. Please try again.')
     }
   }
 
@@ -359,7 +363,7 @@ export function EvaluationForm({
                 <AlertDialogTrigger asChild>
                   <Button
                     type="button"
-                    disabled={!isValid || submit.isPending}
+                    disabled={!isValid || submit.isPending || startEvaluation.isPending}
                   >
                     {submit.isPending ? (
                       <Loader2 className="mr-2 h-4 w-4 animate-spin" />
@@ -678,7 +682,7 @@ export function EvaluationForm({
               <Button
                 type="button"
                 size="lg"
-                disabled={!isValid || submit.isPending}
+                disabled={!isValid || submit.isPending || startEvaluation.isPending}
                 className="w-full sm:w-auto"
               >
                 {submit.isPending ? (