refactor: migrate graph canvas to use web worker for force layout computation

e2e/graph.spec.ts

@@ -62,4 +62,41 @@ test.describe('Graph Canvas', () => {
     const count = await legendItems.count();
     expect(count).toBeGreaterThan(0);
   });
+
+  test('open/close Graph 10x remains responsive (no freeze)', async ({ page }) => {
+    // Capture console errors during the whole test
+    const errors: string[] = [];
+    page.on('console', (msg) => {
+      if (msg.type() === 'error') errors.push(msg.text());
+    });
+
+    // Buttons in header/sidebar
+    const graphButtons = [
+      page.getByRole('button', { name: /graph|graphe/i }).first(),
+    ];
+    const filesButtons = [
+      page.getByRole('button', { name: /files|fichiers/i }).first(),
+    ];
+
+    // Perform 10 rapid toggles
+    for (let i = 0; i < 10; i++) {
+      await graphButtons[0].click({ timeout: 2000 });
+      // Canvas should be present quickly
+      await page.waitForSelector('app-graph-canvas canvas', { timeout: 3000 });
+
+      // Evaluate a trivial script to ensure main thread is not locked
+      const val = await page.evaluate(() => 21 + 21);
+      expect(val).toBe(42);
+
+      // Switch back to files
+      await filesButtons[0].click({ timeout: 2000 });
+
+      // Quick evaluation again
+      const val2 = await page.evaluate(() => 1 + 1);
+      expect(val2).toBe(2);
+    }
+
+    // Ensure no console errors during toggles
+    expect(errors.length).toBeLessThan(2); // allow transient warnings but not repeated errors
+  });
 });