Add .mdb import button and modal with server-side migration runner

public/css/style.css

@@ -311,3 +311,103 @@ td {
   margin-top: auto;
 }
 .form-actions .btn-primary { flex: 1; padding: 8px; }
+
+/* ── Import modal ── */
+.modal-overlay {
+  position: fixed;
+  inset: 0;
+  background: rgba(0,0,0,0.4);
+  z-index: 200;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.15s;
+}
+.modal-overlay.open { opacity: 1; pointer-events: auto; }
+
+.modal {
+  position: fixed;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -48%);
+  width: 480px;
+  max-width: calc(100vw - 2rem);
+  background: var(--surface);
+  border-radius: 6px;
+  box-shadow: 0 8px 32px rgba(0,0,0,0.2);
+  z-index: 201;
+  display: flex;
+  flex-direction: column;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.15s, transform 0.15s;
+}
+.modal.open {
+  opacity: 1;
+  pointer-events: auto;
+  transform: translate(-50%, -50%);
+}
+
+.modal-header {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 10px 16px;
+  background: var(--header-bg);
+  color: var(--header-fg);
+  border-radius: 6px 6px 0 0;
+  flex-shrink: 0;
+}
+.modal-header h2 { font-size: 14px; font-weight: 600; }
+
+.modal-body {
+  padding: 16px;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+.modal-desc {
+  font-size: 12px;
+  color: var(--text-muted);
+  line-height: 1.5;
+}
+.modal-desc code {
+  font-family: monospace;
+  background: var(--bg);
+  padding: 1px 4px;
+  border-radius: 3px;
+}
+
+input[type="file"] {
+  border: 1px solid var(--border);
+  border-radius: 4px;
+  padding: 6px 8px;
+  font-size: 13px;
+  font-family: var(--font);
+  width: 100%;
+  background: var(--surface);
+  cursor: pointer;
+}
+
+.import-log {
+  font-family: monospace;
+  font-size: 11px;
+  background: #0f172a;
+  color: #94a3b8;
+  border-radius: 4px;
+  padding: 10px 12px;
+  max-height: 200px;
+  overflow-y: auto;
+  white-space: pre-wrap;
+  word-break: break-all;
+  line-height: 1.5;
+}
+.import-log.success { color: #86efac; }
+.import-log.error   { color: #fca5a5; }
+
+.modal-footer {
+  display: flex;
+  gap: 8px;
+  padding: 12px 16px;
+  border-top: 1px solid var(--border);
+}