fix: SQLite boolean binding + React StrictMode race condition

- Fix: SqliteAdapter.createLayer/updateLayer: convert JS booleans to integers (true→1, false→0)
  - Root cause: better-sqlite3 cannot bind JS booleans, causing layer creation to fail
  - Without layers, no elements could be created, making the entire CAD editor non-functional
- Fix: loadProjectDataTyped: remove Superseded throw for React StrictMode double-render safety
  - Root cause: StrictMode double-render created two load requests, first was superseded and
    set savedStatus to 'Fehler beim Laden', overwriting the successful second request
- Fix: App.tsx catch block: ignore cancelled/superseded errors to prevent false error status
- All tests pass: Backend 239/239, Frontend 374/374
- UI Test verified: Login → Dashboard → Project → CAD Editor → Line drawing → 4 elements created

frontend/src/App.tsx

@@ -354,6 +354,9 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
           });
         }
       } catch (err) {
+        // Ignore race condition errors from React StrictMode double-render
+        if (cancelled) return;
+        if (err instanceof Error && err.message.includes('Superseded')) return;
         console.error('Failed to load project:', err);
         setSavedStatus('Fehler beim Laden');
       }

frontend/src/services/api.ts

@@ -478,13 +478,7 @@ export async function loadProjectDataTyped(token: string, projectId: string): Pr
       getBlocks(token, drawing.id),
     ]);
 
-    // Only use the result if this is still the latest request for this project
-    const latestRequestId = projectLoadRequestCounter.get(projectId);
-    if (latestRequestId !== currentRequestId) {
-      // A newer request superseded this one — reject to prevent stale data
-      throw new Error('Superseded by a newer load request');
-    }
-
+    // Return data even if a newer request exists (React StrictMode double-render safe)
     return {
       project,
       drawing,