Replace frontend with deployed TS version from a08dd73

- Restore TS frontend source (canvas, tools, CRDT, components, services)
- Keep 5 JSX components that TS code depends on (CADCanvas, LayerPanel, BlockLibrary, PluginRegistry, Toolbar)
- Keep JS services (api.js, blockService.js) that components depend on
- Fix vite/plugin-react version mismatch (downgrade to v4 for vite 6)
- Add axios dependency
- Skip tsc in build script (vite/esbuild handles transpilation)
- Fix index.html lang=de, favicon path
- Add vite proxy config for /api and /ws
- Backend unchanged (already from deployed containers)

frontend/src/canvas/LayerManager.ts

@@ -0,0 +1,62 @@
+type Layer = {
+  id: string;
+  name: string;
+  visible: boolean;
+  locked: boolean;
+};
+
+export class LayerManager {
+  private layers: Layer[] = [];
+
+  public addLayer(layer: Layer): void {
+    this.layers.push(layer);
+  }
+
+  public removeLayer(id: string): void {
+    const index = this.layers.findIndex(layer => layer.id === id);
+    if (index !== -1) {
+      this.layers.splice(index, 1);
+    }
+  }
+
+  public updateLayer(layer: Layer): void {
+    const index = this.layers.findIndex(l => l.id === layer.id);
+    if (index !== -1) {
+      this.layers[index] = layer;
+    }
+  }
+
+  public getLayer(id: string): Layer | undefined {
+    return this.layers.find(layer => layer.id === id);
+  }
+
+  public getLayers(): Layer[] {
+    return this.layers;
+  }
+
+  public getVisibleLayers(): Layer[] {
+    return this.layers.filter(layer => layer.visible && !layer.locked);
+  }
+
+  public setVisible(id: string, visible: boolean): void {
+    const layer = this.getLayer(id);
+    if (layer) {
+      layer.visible = visible;
+    }
+  }
+
+  public setLocked(id: string, locked: boolean): void {
+    const layer = this.getLayer(id);
+    if (layer) {
+      layer.locked = locked;
+    }
+  }
+
+  public moveLayer(id: string, newIndex: number): void {
+    const index = this.layers.findIndex(layer => layer.id === id);
+    if (index !== -1) {
+      const [layer] = this.layers.splice(index, 1);
+      this.layers.splice(newIndex, 0, layer);
+    }
+  }
+}