Add Dockerfile + docker-compose for Coolify deployment

Multi-stage build: node builds the SPA, dotnet publishes the API, the
runtime image serves the SPA from wwwroot/ and exposes /health. Frontend
Supabase URL + publishable key are baked in at build time; DB conn string
and Supabase JWKS metadata come from Coolify env vars. VITE_API_URL empty
means same-origin, so the browser hits /api/todos on the same host that
serves the SPA.

docker-compose.yml

@@ -0,0 +1,25 @@
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+      args:
+        VITE_SUPABASE_URL: ${VITE_SUPABASE_URL}
+        VITE_SUPABASE_PUBLISHABLE_KEY: ${VITE_SUPABASE_PUBLISHABLE_KEY}
+        VITE_API_URL: ""
+    expose:
+      - "8080"
+    environment:
+      SERVICE_FQDN_APP_8080: /
+      ASPNETCORE_ENVIRONMENT: Production
+      ASPNETCORE_URLS: "http://+:8080"
+      ConnectionStrings__Postgres: ${DB_CONNECTION_STRING}
+      Supabase__MetadataAddress: ${SUPABASE_METADATA_ADDRESS}
+      Supabase__Issuer: ${SUPABASE_ISSUER}
+      Supabase__Audience: authenticated
+    healthcheck:
+      test: ["CMD", "curl", "-fsS", "http://127.0.0.1:8080/health"]
+      interval: 30s
+      timeout: 5s
+      retries: 3
+      start_period: 20s