Vendor htmx and add toast/loading-state CSS

Self-hosted htmx v2.0.10 (no CDN) plus the toast container and CSS
this and the following tasks need for in-place sync updates.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/web/static/style.css

@@ -154,6 +154,59 @@ h2 {
     font-size: 0.78rem;
 }
 
+.toast-container {
+    position: fixed;
+    top: 1rem;
+    right: 1rem;
+    z-index: 100;
+    display: flex;
+    flex-direction: column;
+    gap: 0.5rem;
+    pointer-events: none;
+}
+
+.toast {
+    pointer-events: auto;
+    background: var(--surface-raised);
+    border: 1px solid var(--border);
+    border-left: 3px solid var(--text-muted);
+    border-radius: 8px;
+    padding: 0.6rem 0.9rem;
+    font-size: 0.85rem;
+    color: var(--text);
+    box-shadow: 0 4px 16px rgba(0, 0, 0, 0.3);
+    max-width: 320px;
+    transition: opacity 200ms ease, transform 200ms ease;
+}
+
+.toast-success {
+    border-left-color: var(--success);
+}
+
+.toast-danger {
+    border-left-color: var(--danger);
+}
+
+.toast-info {
+    border-left-color: var(--info);
+}
+
+.toast-leaving {
+    opacity: 0;
+    transform: translateX(8px);
+}
+
+@media (prefers-reduced-motion: reduce) {
+    .toast {
+        transition: none;
+    }
+}
+
+button.htmx-request, .btn.htmx-request {
+    opacity: 0.6;
+    cursor: progress;
+}
+
 .card {
     background: var(--surface);
     border: 1px solid var(--border);