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/slug.ts

@@ -0,0 +1,9 @@
+export function generateSlug(title: string): string {
+  return title
+    .toLowerCase()
+    .replace(/[^a-z0-9]+/g, "-")
+    .replace(/-+/g, "-")
+    .replace(/^-|-$/g, "")
+    .slice(0, 80)
+    .replace(/-$/g, "")
+}