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/interaction/SnapEngine.ts

@@ -0,0 +1,86 @@
+class SnapEngine {
+  private isEnabled: boolean;
+  private gridSize: number;
+  private tolerance: number;
+  private activeZoom: number;
+
+  constructor(gridSize: number = 10) {
+    this.isEnabled = true;
+    this.gridSize = gridSize;
+    this.tolerance = 5;
+    this.activeZoom = 1;
+  }
+
+  // Toggle snap on/off with F3
+  toggleSnap(): void {
+    this.isEnabled = !this.isEnabled;
+  }
+
+  // Set active zoom level
+  setZoom(zoom: number): void {
+    this.activeZoom = zoom;
+  }
+
+  // Snap to grid
+  snapToGrid(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to grid
+    return null;
+  }
+
+  // Snap to endpoint
+  snapToEndpoint(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to endpoint
+    return null;
+  }
+
+  // Snap to midpoint
+  snapToMidpoint(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to midpoint
+    return null;
+  }
+
+  // Snap to center
+  snapToCenter(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to center
+    return null;
+  }
+
+  // Snap to intersection
+  snapToIntersection(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to intersection
+    return null;
+  }
+
+  // Snap to perpendicular
+  snapToPerpendicular(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to perpendicular
+    return null;
+  }
+
+  // Snap to tangent
+  snapToTangent(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to tangent
+    return null;
+  }
+
+  // Snap to nearest
+  snapToNearest(x: number, y: number): {x: number, y: number} | null {
+    if (!this.isEnabled) return null;
+    // Implementation for snap to nearest
+    return null;
+  }
+
+  // Render visual snap markers on canvas
+  renderSnapMarkers(context: CanvasRenderingContext2D): void {
+    // Implementation for rendering snap markers
+  }
+}
+
+export default SnapEngine;