feat: upload file in contact form

static/css/main.css

@@ -2530,6 +2530,38 @@ a.citation-count-badge:hover {
   margin-left: 0.25rem;
 }
 
+.form-hint {
+  font-size: 0.78rem;
+  color: var(--text-muted, var(--text-secondary));
+  margin-top: 0.35rem;
+  line-height: 1.4;
+}
+
+.form-file-list {
+  font-size: 0.82rem;
+  color: var(--text-secondary);
+  margin-top: 0.35rem;
+  min-height: 1.2em;
+}
+
+.form-group input[type="file"] {
+  padding: 0.55rem 0.75rem;
+  cursor: pointer;
+}
+
+.form-group input[type="file"]::file-selector-button {
+  margin-right: 0.75rem;
+  padding: 0.4rem 0.85rem;
+  border-radius: var(--radius-sm);
+  border: 1px solid var(--glass-border);
+  background: rgba(79, 142, 247, 0.12);
+  color: var(--text-primary);
+  font-family: inherit;
+  font-size: 0.82rem;
+  font-weight: 600;
+  cursor: pointer;
+}
+
 .form-group input,
 .form-group textarea,
 .form-group select {
@@ -2560,7 +2592,8 @@ a.citation-count-badge:hover {
 }
 
 .form-group.has-error input,
-.form-group.has-error textarea {
+.form-group.has-error textarea,
+.form-group.has-error input[type="file"] {
   border-color: rgba(239, 68, 68, 0.5);
   box-shadow: 0 0 0 3px rgba(239, 68, 68, 0.1);
 }