feat: scaffold klarbild foundation (astro+postgres+s3, auth, migrations, health)

- Astro 5 SSR (node standalone) + React, OKLCH tokens (no tailwind)
- migrations/001_init.sql: full schema per 03-datenmodell-api
- lib: db+migrations, crypto (AES-256-GCM), auth (argon2+signed session, ratelimit),
  storage (S3/MinIO, presigned URLs), openrouter (POST /v1/images, cost)
- middleware: init-once + session guard + admin gate; /api/health (db+storage)
- login + studio placeholder; seeds (till/lea, default recipes); Dockerfile
- verified: astro build passes

astro.config.mjs

@@ -0,0 +1,17 @@
+import { defineConfig } from 'astro/config';
+import node from '@astrojs/node';
+import react from '@astrojs/react';
+
+// Klarbild läuft als Node-Server (SSR) mit In-Process-Warteschlange.
+export default defineConfig({
+  output: 'server',
+  adapter: node({ mode: 'standalone' }),
+  integrations: [react()],
+  server: { host: true, port: Number(process.env.PORT) || 4321 },
+  vite: {
+    ssr: {
+      // Native Module nicht bündeln
+      external: ['sharp', 'argon2', 'pg', 'pg-boss', 'ssh2-sftp-client', 'basic-ftp', 'heic-convert'],
+    },
+  },
+});