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/lib/utils.ts

@@ -0,0 +1,8 @@
+/**
+ * Simple class name utility that filters out falsy values and joins with spaces.
+ * This is a lightweight alternative to clsx/tailwind-merge for projects that
+ * don't need the full complexity of those libraries.
+ */
+export function cn(...inputs: (string | boolean | undefined | null)[]): string {
+  return inputs.filter(Boolean).join(" ");
+}