feat: enhance dashboard and canvas components with improved state management and resizing logic

- Added client mount state to the dashboard to prevent premature interactions before the component is fully loaded.
- Updated button disabling logic to ensure it reflects the component's readiness and user session state.
- Introduced zIndex handling in canvas placement context for better node layering.
- Enhanced asset and image nodes with improved resizing logic to maintain aspect ratios during adjustments.
- Refactored node components to streamline rendering and improve performance during dynamic updates.

components/canvas/connection-banner.tsx

@@ -104,7 +104,8 @@ export default function ConnectionBanner() {
       return showReconnected ? "reconnected" : "hidden";
     }
 
-    if (!isBrowserOnline) {
+    // Streng `=== false`, damit kein undefined/SSR-Artefakt wie „offline“ wird.
+    if (isBrowserOnline === false) {
       return "disconnected";
     }
 
@@ -121,6 +122,12 @@ export default function ConnectionBanner() {
     showReconnected,
   ]);
 
+  // WebSocket/Convex-Verbindung gibt es im Browser; SSR soll keinen Banner rendern,
+  // sonst weicht die Geschwister-Reihenfolge vom ersten Client-Render ab (Hydration).
+  if (typeof window === "undefined") {
+    return null;
+  }
+
   if (bannerState === "hidden") {
     return null;
   }