Chart theming: custom named themes + Theme Builder

src/app/infrastructure/theme-migrations.ts

@@ -0,0 +1,25 @@
+/**
+ * Read-time migration for CustomTheme records (docs/architecture/02 §4).
+ *
+ * Mirrors snippet/dataset migrations: every theme read from storage passes
+ * through `migrateCustomTheme`, which fills missing/invalid fields and stamps
+ * the current version. Unknown fields are tolerated (spread the original, only
+ * fill gaps) so a record written by a newer build round-trips without loss.
+ */
+
+import { CURRENT_THEME_VERSION, type CustomTheme } from '@core/custom-theme';
+import { isJsonObject } from '@core/spec-config';
+
+/** Upgrade a raw stored record to the current CustomTheme shape. */
+export function migrateCustomTheme(raw: unknown): CustomTheme {
+  const r = { ...(raw as Record<string, unknown>) };
+  return {
+    ...r,
+    id: typeof r.id === 'number' ? r.id : Number(r.id),
+    version: CURRENT_THEME_VERSION,
+    name: typeof r.name === 'string' ? r.name : 'Untitled theme',
+    config: isJsonObject(r.config) ? r.config : {},
+    created: typeof r.created === 'string' ? r.created : new Date(0).toISOString(),
+    modified: typeof r.modified === 'string' ? r.modified : new Date(0).toISOString(),
+  };
+}