Add admin panel, WebSocket support, and API versioning

Introduce an admin portal (React + Nginx), WebSocket routing, and
API versioning middleware with `/api/v1/` prefix deprecation.
Add master API key authentication, new Prometheus metrics for AI
token consumption and active WebSockets, and extend S3 config
with a public endpoint URL. Update test paths and fixtures to
align with the new routing structure.

imago-admin/postcss.config.js

@@ -0,0 +1,6 @@
+export default {
+    plugins: {
+        tailwindcss: {},
+        autoprefixer: {},
+    },
+};