Add instant fiber availability check to website

Adds a quick address/postal code lookup that queries
intra.cuitunet.fi API to show if fiber is available,
directly in the contact section.

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

style.css

@@ -556,6 +556,82 @@ img {
     box-shadow: 0 0 0 3px rgba(232, 137, 29, 0.1);
 }
 
+/* ---- Availability Check ---- */
+.availability-check {
+    margin-top: 32px;
+    background: var(--bg);
+    border: 1px solid var(--border);
+    border-radius: var(--radius);
+    padding: 24px;
+}
+
+.availability-check h3 {
+    font-size: 1rem;
+    font-weight: 600;
+    color: var(--dark);
+    margin-bottom: 12px;
+}
+
+.availability-check-form {
+    display: flex;
+    gap: 8px;
+}
+
+.availability-check-form input {
+    flex: 1;
+    padding: 11px 14px;
+    border: 1.5px solid var(--border);
+    border-radius: 8px;
+    font-size: 0.95rem;
+    font-family: inherit;
+    transition: border-color 0.2s, box-shadow 0.2s;
+}
+
+.availability-check-form input:focus {
+    outline: none;
+    border-color: var(--orange);
+    box-shadow: 0 0 0 3px rgba(232, 137, 29, 0.1);
+}
+
+.check-result {
+    margin-top: 12px;
+    padding: 14px 16px;
+    border-radius: 8px;
+    font-size: 0.9rem;
+    line-height: 1.5;
+}
+
+.check-result.ok {
+    background: #ecfdf5;
+    border: 1px solid #a7f3d0;
+    color: #065f46;
+}
+
+.check-result.nok {
+    background: #fef2f2;
+    border: 1px solid #fecaca;
+    color: #991b1b;
+}
+
+.check-result.loading {
+    background: var(--bg-alt);
+    border: 1px solid var(--border);
+    color: var(--text-light);
+}
+
+.check-result h4 {
+    font-size: 0.95rem;
+    margin-bottom: 4px;
+}
+
+.check-result-address {
+    background: rgba(255,255,255,0.6);
+    padding: 6px 10px;
+    border-radius: 6px;
+    margin-top: 6px;
+    font-size: 0.85rem;
+}
+
 /* ---- Footer ---- */
 .footer {
     background: var(--dark-soft);