feat: add bar width multiplier (1x–8x horizontal zoom) for track grid

src/core/project-upgrader/KGProjectUpgrader.ts

@@ -3,6 +3,7 @@ import { upgradeToV1 } from './upgradeToV1';
 import { upgradeToV2 } from './upgradeToV2';
 import { upgradeToV3 } from './upgradeToV3';
 import { upgradeToV4 } from './upgradeToV4';
+import { upgradeToV5 } from './upgradeToV5';
 
 /**
  * Upgrade the given project to the latest structure version, one version at a time.
@@ -38,6 +39,10 @@ export function upgradeProjectToLatest(project: KGProject): KGProject {
         workingProject = upgradeToV4(workingProject);
         break;
       }
+      case 5: {
+        workingProject = upgradeToV5(workingProject);
+        break;
+      }
       default: {
         // If an upgrader is missing, throw to prevent loading incompatible structures
         throw new Error(`No upgrader found for project structure version ${nextVersion}`);

src/core/project-upgrader/upgradeToV5.ts

@@ -0,0 +1,13 @@
+import { KGProject } from '../KGProject';
+
+export function upgradeToV5(project: KGProject): KGProject {
+  try {
+    const current = project.getBarWidthMultiplier?.();
+    if (current === undefined || current === null) {
+      project.setBarWidthMultiplier(1);
+    }
+  } finally {
+    project.setProjectStructureVersion(5);
+  }
+  return project;
+}