feat: add loading indicators for long-running operations

Add loading overlay to sessions list during create, stop, delete,
and recreate tunnel operations. Show progress messages like
'Creating instance...' and 'Starting container...' during creation.
Dim the sessions grid while operations are in progress to prevent
user confusion and accidental duplicate actions.

apps/web/src/styles.css

@@ -2717,6 +2717,62 @@ a.nav-item,
   margin-bottom: var(--space-6);
 }
 
+/* Loading overlay for sessions */
+.sessions-grid {
+  position: relative;
+}
+
+.sessions-grid.dimmed {
+  opacity: 0.5;
+  pointer-events: none;
+}
+
+.loading-overlay {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  z-index: 10;
+  background: rgba(255, 254, 249, 0.7);
+  border-radius: var(--space-2);
+}
+
+.loading-content {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: var(--space-3);
+  padding: var(--space-6);
+  background: var(--panel);
+  border: 1px solid var(--border);
+  border-radius: var(--space-2);
+  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
+}
+
+.loading-content .icon {
+  animation: spin 1s linear infinite;
+  color: var(--brand);
+}
+
+.loading-content p {
+  margin: 0;
+  font-size: var(--font-size-base);
+  color: var(--muted);
+}
+
+@keyframes spin {
+  from {
+    transform: rotate(0deg);
+  }
+  to {
+    transform: rotate(360deg);
+  }
+}
+
 .recent-sessions-list {
   display: flex;
   flex-direction: column;