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/.dockerignore

@@ -0,0 +1,12 @@
+node_modules
+dist
+.git
+.gitignore
+*.md
+*.test.ts
+*.test.tsx
+.env
+.env.*
+.vscode
+.idea
+coverage