Fix Zitadel dev setup: use login v1 and add healthcheck

- Switch image to ghcr.io/zitadel/zitadel:latest (v4.x)
- Disable login v2 (LOGINV2_REQUIRED: false) to use built-in login v1
- Add curl-based healthcheck for reliable container readiness

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker/docker-compose.dev.yml

@@ -1,6 +1,6 @@
 services:
   zitadel:
-    image: ghcr.io/zitadel/zitadel:v3-latest
+    image: ghcr.io/zitadel/zitadel:latest
     command: start-from-init --masterkey "${ZITADEL_MASTERKEY}" --tlsMode disabled
     environment:
       ZITADEL_DATABASE_POSTGRES_HOST: zitadel-db
@@ -18,11 +18,18 @@ services:
       ZITADEL_TLS_MODE: disabled
       ZITADEL_FIRSTINSTANCE_ORG_HUMAN_USERNAME: admin
       ZITADEL_FIRSTINSTANCE_ORG_HUMAN_PASSWORD: "${ZITADEL_ADMIN_PASSWORD}"
+      ZITADEL_DEFAULTINSTANCE_FEATURES_LOGINV2_REQUIRED: "false"
     ports:
       - "8080:8080"
     depends_on:
       zitadel-db:
         condition: service_healthy
+    healthcheck:
+      test: ["CMD", "curl", "-sf", "http://localhost:8080/debug/healthz"]
+      interval: 10s
+      timeout: 5s
+      retries: 15
+      start_period: 30s
     restart: unless-stopped
 
   zitadel-db: