fix: review fixes — IMAGE_PULL_SECRETS, SCW registry, devpod provider

- Add missing IMAGE_PULL_SECRETS=gitlab-registry to devpod-setup.sh
- CI job pushes devcontainer to SCW registry (not internal GitLab)
- Remove unused internal registry auth from build-devcontainer job
- Add customizations.devpod.provider to devcontainer.json

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

.devcontainer/devcontainer.json

@@ -14,5 +14,10 @@
     "EDITOR": "vim"
   },
   "postCreateCommand": "/usr/local/bin/init-home.sh",
-  "postStartCommand": "claude --version && cargo --version && kubectl cluster-info 2>/dev/null || true"
+  "postStartCommand": "claude --version && cargo --version && kubectl cluster-info 2>/dev/null || true",
+  "customizations": {
+    "devpod": {
+      "provider": "kubernetes"
+    }
+  }
 }