excalidraw: grant emo-browser SA port-forward for drawing uploads

Viktor asked to fix emo's permission so his Claude can upload to the
Excalidraw service. emo's recent sessions show the documented upload
recipe (kubectl port-forward svc/draw + X-Authentik-Username header,
from his ~/.claude/CLAUDE.md) failing with:

  pods/portforward forbidden for system:serviceaccount:chrome-service:emo-browser
  in namespace excalidraw

because his default kubeconfig is the read-only emo-browser SA (its
port-forward grant covers only chrome-service) and his old admin
kubeconfig at /home/emo/code/config expired and was removed.

Add a namespace-scoped Role (pods/portforward create) + RoleBinding for
that SA in the excalidraw namespace, mirroring the 2026-06-28
chrome-service grant. Trade-off (any-user drawings via the trusted
username header) documented in the file and accepted.

Also record the grant in docs/architecture/chrome-service.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

stacks/excalidraw/rbac.tf

@@ -0,0 +1,49 @@
+# emo's Claude → Excalidraw upload RBAC.
+#
+# emo's agent uploads drawings with `kubectl -n excalidraw port-forward svc/draw`
+# + `PUT /api/drawings/<name>` carrying the X-Authentik-Username header (the
+# documented recipe in emo's ~/.claude/CLAUDE.md — the app sits behind Authentik
+# forward-auth, so direct curl gets redirected). His hands-off credential is the
+# chrome-service/emo-browser ServiceAccount kubeconfig (stacks/chrome-service/rbac.tf);
+# its cluster-wide grant (oidc-power-user-readonly) is read-only, so pods/portforward
+# must be granted per namespace. This is the excalidraw-namespace grant
+# (Viktor's call, 2026-07-02; same pattern as the chrome-service one).
+#
+# TRADE-OFF (accepted): port-forward into this namespace bypasses the Authentik
+# ingress and the drawings API trusts the X-Authentik-Username header, so the SA
+# can read/write ANY user's drawings, not only emo's. The namespace runs nothing
+# but the drawings app, and the same class of trade-off was already accepted for
+# the shared browser (CDP reach into Viktor's sessions).
+
+resource "kubernetes_role" "portforward" {
+  metadata {
+    name      = "excalidraw-portforward"
+    namespace = kubernetes_namespace.excalidraw.metadata[0].name
+  }
+  rule {
+    api_groups = [""]
+    resources  = ["pods/portforward"]
+    verbs      = ["create"]
+  }
+}
+
+resource "kubernetes_role_binding" "emo_browser_portforward" {
+  metadata {
+    name      = "emo-browser-portforward"
+    namespace = kubernetes_namespace.excalidraw.metadata[0].name
+  }
+  role_ref {
+    api_group = "rbac.authorization.k8s.io"
+    kind      = "Role"
+    name      = kubernetes_role.portforward.metadata[0].name
+  }
+  subject {
+    kind = "ServiceAccount"
+    # Defined in stacks/chrome-service/rbac.tf — referenced by name across
+    # stacks, same as that file references the oidc-power-user-readonly
+    # ClusterRole. get/list on pods+services (needed to resolve svc/draw) comes
+    # from the SA's cluster-read binding there.
+    name      = "emo-browser"
+    namespace = "chrome-service"
+  }
+}