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

packages/shared/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "composite": true,
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "outDir": "./dist",
+    "rootDir": "./src"
+  },
+  "include": ["src"]
+}