fix(audit-wave-9): unified template token picker with custom-field group

Build a shared <TemplateTokenPicker> that renders the canonical
MERGE_FIELDS catalog grouped by scope, plus a dynamically-fetched
"Custom (port-specific)" group surfaced from /api/v1/admin/custom-fields.
The custom group is filtered to entity types the resolver actually
expands at send time (client/interest/berth - see
mergeCustomFieldValues in document-sends.service).

Wire it into both consumers:
- admin/document-templates/template-form.tsx (replaces TEMPLATE_VARIABLES
  list which had drifted from the canonical catalog)
- admin/sales-email-config-card.tsx (replaces flat alphabetical dump)

Closes custom-fields §B "UI surfacing of {{custom.…}} tokens".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/admin/sales-email-config-card.tsx

@@ -23,7 +23,7 @@ import { Label } from '@/components/ui/label';
 import { Switch } from '@/components/ui/switch';
 import { Textarea } from '@/components/ui/textarea';
 import { apiFetch } from '@/lib/api/client';
-import { VALID_MERGE_TOKENS } from '@/lib/templates/merge-fields';
+import { TemplateTokenPicker } from '@/components/admin/shared/template-token-picker';
 import { toastError } from '@/lib/api/toast-error';
 
 interface SalesConfigResponse {
@@ -313,14 +313,10 @@ export function SalesEmailConfigCard() {
         <CardContent className="space-y-4">
           <details className="rounded-md border bg-muted/30 px-3 py-2 text-xs">
             <summary className="cursor-pointer font-medium text-foreground">
-              Available tokens ({Array.from(VALID_MERGE_TOKENS).length})
+              Available tokens
             </summary>
-            <div className="mt-2 grid grid-cols-2 gap-x-3 gap-y-0.5 font-mono text-[11px] text-muted-foreground sm:grid-cols-3">
-              {Array.from(VALID_MERGE_TOKENS)
-                .sort()
-                .map((tok) => (
-                  <span key={tok}>{tok}</span>
-                ))}
+            <div className="mt-3">
+              <TemplateTokenPicker />
             </div>
           </details>
           <Field