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

plugins/decky-vault/rollup.config.js

@@ -0,0 +1,20 @@
+import typescript from "@rollup/plugin-typescript"
+import commonjs from "@rollup/plugin-commonjs"
+
+export default {
+  input: "src/index.tsx",
+  output: {
+    file: "dist/index.js",
+    format: "esm",
+    sourcemap: false,
+  },
+  plugins: [
+    typescript(),
+    commonjs(),
+  ],
+  external: [
+    "react",
+    "react-dom",
+    "@deckyvault/shared",
+  ],
+}