feat: add "+ App" shortcut button to sidebar Applications header

Adds a subtle "+ App" button in the sidebar section header for quick
app creation without navigating to the Deployments tab first. Only
visible to OPERATOR and ADMIN roles.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/LayoutShell.module.css

@@ -43,6 +43,34 @@
   opacity: 0.6;
 }
 
+.appSectionWrap {
+  position: relative;
+}
+
+.addAppBtn {
+  position: absolute;
+  top: 6px;
+  right: 6px;
+  z-index: 1;
+  display: flex;
+  align-items: center;
+  gap: 2px;
+  background: none;
+  border: none;
+  padding: 2px 6px;
+  border-radius: 4px;
+  font-size: 12px;
+  font-weight: 500;
+  color: var(--sidebar-muted);
+  cursor: pointer;
+  transition: color 0.12s, background 0.12s;
+}
+
+.addAppBtn:hover {
+  color: var(--amber);
+  background: rgba(255, 255, 255, 0.06);
+}
+
 .mainContent {
   flex: 1;
   display: flex;