Add ArgoCD GitOps bootstrap contract for railiance01

Define platform-owned AppProjects, root app-of-apps, repository registration
templates, and tenant onboarding docs so issue-core can deploy via ArgoCD.
Ignore encrypted repository secrets locally and cross-link OpenBao delivery
guidance with the new GitOps contract.

argocd/repositories/README.md

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+# ArgoCD Repository Registration
+
+ArgoCD discovers Git repositories from Kubernetes Secrets in the `argocd`
+namespace with `argocd.argoproj.io/secret-type: repository`.
+
+Use the templates in this directory to create SOPS-encrypted, non-plaintext
+repository Secret files. Credentials must be sourced from the approved
+operator/OpenBao path and must never be committed in plaintext.
+
+Recommended OpenBao path:
+
+```text
+platform/operators/argocd/repositories/<repo-name>
+```
+
+After creating an encrypted file such as
+`argocd/repositories/railiance-platform.repository.sops.yaml`, apply it with:
+
+```bash
+ARGOCD_REPOSITORY_SECRET=argocd/repositories/railiance-platform.repository.sops.yaml \
+  make argocd-repo-apply
+```
+

argocd/repositories/issue-core.repository.sops.yaml.template

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+# Copy to issue-core.repository.sops.yaml, fill from the approved
+# operator/OpenBao path, then encrypt with:
+#   sops -e -i argocd/repositories/issue-core.repository.sops.yaml
+#
+# Do not commit plaintext credentials.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: issue-core-repository
+  namespace: argocd
+  labels:
+    argocd.argoproj.io/secret-type: repository
+    app.kubernetes.io/part-of: railiance-gitops
+    railiance-platform/component: gitops
+stringData:
+  type: git
+  project: railiance-tenants
+  url: https://gitea.coulomb.social/coulomb/issue-core.git
+  username: CHANGE_ME
+  password: CHANGE_ME
+

argocd/repositories/railiance-platform.repository.sops.yaml.template

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+# Copy to railiance-platform.repository.sops.yaml, fill from the approved
+# operator/OpenBao path, then encrypt with:
+#   sops -e -i argocd/repositories/railiance-platform.repository.sops.yaml
+#
+# Do not commit plaintext credentials.
+apiVersion: v1
+kind: Secret
+metadata:
+  name: railiance-platform-repository
+  namespace: argocd
+  labels:
+    argocd.argoproj.io/secret-type: repository
+    app.kubernetes.io/part-of: railiance-gitops
+    railiance-platform/component: gitops
+stringData:
+  type: git
+  project: railiance-bootstrap
+  url: https://gitea.coulomb.social/coulomb/railiance-platform.git
+  username: CHANGE_ME
+  password: CHANGE_ME
+