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/index.html

@@ -0,0 +1,18 @@
+<!doctype html>
+<html lang="fr" class="dark">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/favicon.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta name="description" content="Portail d'administration et de surveillance pour Imago Hub — gestion d'images avec pipeline AI multi-clients" />
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
+    <link rel="preconnect" href="https://fonts.gstatic.com" crossOrigin="" />
+    <link href="https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=JetBrains+Mono:wght@400;500&display=swap" rel="stylesheet" />
+    <link rel="stylesheet" href="https://unpkg.com/[email protected]/dist/leaflet.css" />
+    <title>Imago Hub Admin</title>
+  </head>
+  <body class="bg-surface text-content-primary antialiased">
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>