feat: embed frontend into backend server with full-stack build pipeline (RCA-20)

The backend now serves the Vue admin UI as static files with SPA fallback,
eliminating the need for a separate web server. Dockerfile builds both
frontend and backend in a multi-stage pipeline. Added build:web and
build:all scripts, updated CI to verify frontend builds, and fixed
vitest config to exclude Playwright tests.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/cli.ts

@@ -1,3 +1,5 @@
+import path from "node:path";
+import fs from "node:fs";
 import { RelayServer } from "./relay/index.js";
 import { loadDbConfig, createStores } from "./relay/db/index.js";
 
@@ -16,10 +18,28 @@ async function main() {
     console.log("Configure a database during setup to enable persistent storage.");
   }
 
-  const server = new RelayServer({ port, host, stores });
+  // Resolve frontend public directory: check ./public (production) then ../web/dist (development)
+  let publicDir: string | undefined;
+  const candidates = [
+    path.resolve("public"),
+    path.resolve(__dirname, "..", "web", "dist"),
+  ];
+  for (const dir of candidates) {
+    if (fs.existsSync(path.join(dir, "index.html"))) {
+      publicDir = dir;
+      break;
+    }
+  }
+
+  const server = new RelayServer({ port, host, stores, publicDir });
 
   await server.start();
   console.log(`CookieBridge relay server listening on ${host}:${port}`);
+  if (publicDir) {
+    console.log(`Serving admin UI from ${publicDir}`);
+  } else {
+    console.log("No frontend build found — admin UI not available. Run: npm run build:web");
+  }
 
   process.on("SIGINT", async () => {
     console.log("\nShutting down...");