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/public/.well-known/apple-app-site-association

@@ -0,0 +1,6 @@
+{
+  "applinks": {},
+  "webcredentials": {
+    "apps": ["YOUR_TEAM_ID.xyz.deckyvault.app"]
+  }
+}

apps/web/public/.well-known/assetlinks.json

@@ -0,0 +1,15 @@
+[
+  {
+    "relation": [
+      "delegate_permission/common.handle_all_urls",
+      "delegate_permission/common.get_login_creds"
+    ],
+    "target": {
+      "namespace": "android_app",
+      "package_name": "xyz.deckyvault.app",
+      "sha256_cert_fingerprints": [
+        "YOUR_SHA256_FINGERPRINT"
+      ]
+    }
+  }
+]