Fix contact form styles + narrow screen nav clipping

- Alias .form-group to .form-field in main.css so contact form inputs get full styling
- Hide header Get Estimate btn on <=480px (mobile drawer has CTA, prevents logo+btn+hamburger overflow)
- Tighten header-inner gap to space-4 on <=480px
- Drop redundant btn-sm padding override from 360px rule (btn now hidden at that width)

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

assets/css/main.css

@@ -238,13 +238,15 @@ p { max-width: 68ch; }
 }
 .form-grid--2 { grid-template-columns: repeat(auto-fit, minmax(min(100%, 260px), 1fr)); }
 
-.form-field {
+.form-field,
+.form-group {
   display: flex;
   flex-direction: column;
   gap: var(--space-2);
 }
 
-.form-field label {
+.form-field label,
+.form-group label {
   font-size: var(--text-sm);
   font-weight: 600;
   letter-spacing: 0.02em;
@@ -253,7 +255,10 @@ p { max-width: 68ch; }
 
 .form-field input,
 .form-field textarea,
-.form-field select {
+.form-field select,
+.form-group input,
+.form-group textarea,
+.form-group select {
   width: 100%;
   padding: 0.875rem 1rem;
   background: var(--white);
@@ -268,15 +273,21 @@ p { max-width: 68ch; }
 
 .form-field input:focus,
 .form-field textarea:focus,
-.form-field select:focus {
+.form-field select:focus,
+.form-group input:focus,
+.form-group textarea:focus,
+.form-group select:focus {
   border-color: var(--amber);
   box-shadow: 0 0 0 3px rgba(200,139,42,0.15);
 }
 
-.form-field input.valid { border-color: #2d9e57; }
-.form-field input.invalid { border-color: #c0392b; }
+.form-field input.valid,
+.form-group input.valid { border-color: #2d9e57; }
+.form-field input.invalid,
+.form-group input.invalid { border-color: #c0392b; }
 
-.form-field textarea {
+.form-field textarea,
+.form-group textarea {
   min-height: 130px;
   resize: vertical;
 }