feat: deploy all stacks to shared ai-stack-portal project

- Add SHARED_PROJECT_ID and SHARED_ENVIRONMENT_ID env vars
- Add findApplicationByName to Dokploy client for app-based lookup
- Update production-deployer to use shared project instead of creating new ones
- Update name availability check to query apps in shared environment
- Update delete endpoint to remove apps from shared project
- Rollback no longer deletes shared project (only app/domain)
- Backward compatible: falls back to per-project if env vars not set

.env.example

@@ -18,7 +18,13 @@ DOKPLOY_API_TOKEN=
 
 # Stack Configuration
 STACK_DOMAIN_SUFFIX=ai.flexinit.nl
-STACK_IMAGE=git.app.flexinit.nl/oussamadouhou/oh-my-opencode-free:latest
+STACK_IMAGE=git.app.flexinit.nl/flexinit/agent-stack:latest
+STACK_REGISTRY_ID=
+
+# Shared Project Deployment (all stacks deploy to one Dokploy project)
+# Project: ai-stack-portal, Environment: deployments
+SHARED_PROJECT_ID=2y2Glhz5Wy0dBNf6BOR_-
+SHARED_ENVIRONMENT_ID=RqE9OFMdLwkzN7pif1xN8
 
 # Traefik Public IP (where DNS records should point)
 TRAEFIK_IP=144.76.116.169