Replace from-scratch rewrite with real ngoduykhanh/wireguard-ui fork

The from-scratch Go rewrite had unresolved bugs (missing go.sum, UI
404s, path issues) from being built without a working local Go
toolchain to verify against. Switching strategy: use the actual
upstream wireguard-ui codebase (proven, battle-tested single-server
manager) as the base, and extend it for multi-server support instead
of re-deriving everything from zero.

Kept our own installers (bootstrap.sh, update.sh, scripts/install.sh,
scripts/proxmox-install.sh) - these still apply, just need updating
to build/install the upstream module layout instead of the old
cmd/wireguard-ui-multi structure.

Module path intentionally left as upstream's own
(github.com/ngoduykhanh/wireguard-ui) for now to avoid touching every
internal import; revisit if this needs to be fully rebranded.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

package.json

@@ -0,0 +1,13 @@
+{
+  "name": "wireguard-ui",
+  "version": "1.0.0",
+  "description": "Wireguard web interface",
+  "main": "index.js",
+  "repository": "git@github.com:ngoduykhanh/wireguard-ui.git",
+  "author": "Khanh Ngo <k@ndk.name>",
+  "license": "MIT",
+  "dependencies": {
+    "admin-lte": "^3.0",
+    "jquery-tags-input": "^1.3.5"
+  }
+}