feat(k8s): publish the portals through the labs Caddy (refs #177)

Adds a `keycloakUrl` chart value: when set, it replaces host + Keycloak's
NodePort as the pinned issuer and the portals' OIDC authority, so the stack
works behind the existing *.labs.respellion.tech Caddy over HTTPS. Empty keeps
today's behaviour. The deploy workflow passes the KEYCLOAK_URL repo variable.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

.gitea/workflows/deploy.yaml

@@ -27,6 +27,10 @@ jobs:
       # `kubectl port-forward` — runbook §5. Override with repo variables.
       TALOS_VM_IP: ${{ vars.TALOS_VM_IP }}
       TALOS_HOST: ${{ vars.TALOS_HOST }}
+      # Set it when the labs Caddy publishes the portals: Keycloak's public https
+      # origin, e.g. https://big-auth.labs.respellion.tech (runbook, "Publishing
+      # through the labs Caddy").
+      KEYCLOAK_URL: ${{ vars.KEYCLOAK_URL }}
     steps:
       - uses: https://github.com/actions/checkout@v4
 
@@ -89,7 +93,11 @@ jobs:
       # The jobs are idempotent, and deleting them first is what keeps a changed
       # Job template from wedging the upgrade (`cannot patch … with kind Job`).
       - name: Deploy the chart
-        run: make k8s-reseed TALOS_HOST=${TALOS_HOST:-localhost} K8S_REGISTRY=${TALOS_VM_IP:-192.168.122.173}:30500
+        run: |
+          make k8s-reseed \
+            TALOS_HOST=${TALOS_HOST:-localhost} \
+            K8S_REGISTRY=${TALOS_VM_IP:-192.168.122.173}:30500 \
+            K8S_SET="${KEYCLOAK_URL:+--set keycloakUrl=$KEYCLOAK_URL}"
 
       # `dev` is a mutable tag and helm sees an unchanged pod template, so the
       # new images only land on a restart (pullPolicy is already Always).