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/app/api/[[...slugs]]/route.ts

@@ -0,0 +1,7 @@
+import { app } from "@/lib/api/app"
+
+export const GET = app.fetch
+export const POST = app.fetch
+export const PUT = app.fetch
+export const DELETE = app.fetch
+export const PATCH = app.fetch