refactor: convert to bun workspaces monorepo

- Move web app into apps/web/
- Create packages/shared/ with shared types
- Create plugins/decky-vault/ scaffold
- Root package.json manages workspaces only

apps/web/components/manage/dashboard-charts.tsx

@@ -0,0 +1,7 @@
+"use client";
+
+// Future: ECharts integration for trends over time
+// For now, the overview stats are sufficient
+export function DashboardCharts() {
+  return null;
+}