Update availability check: require full address, show only yes/no

Three fields (address, zip, city) instead of one. API now returns
only true/false, no addresses or speeds exposed publicly.

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

style.css

@@ -572,13 +572,19 @@ img {
     margin-bottom: 12px;
 }
 
-.availability-check-form {
+.availability-check-fields {
     display: flex;
+    flex-direction: column;
     gap: 8px;
 }
 
-.availability-check-form input {
-    flex: 1;
+.availability-check-row {
+    display: grid;
+    grid-template-columns: 1fr 1fr;
+    gap: 8px;
+}
+
+.availability-check-fields input {
     padding: 11px 14px;
     border: 1.5px solid var(--border);
     border-radius: 8px;
@@ -587,7 +593,7 @@ img {
     transition: border-color 0.2s, box-shadow 0.2s;
 }
 
-.availability-check-form input:focus {
+.availability-check-fields input:focus {
     outline: none;
     border-color: var(--orange);
     box-shadow: 0 0 0 3px rgba(232, 137, 29, 0.1);