Import minecraft-router chart unchanged (Fleet migration stage 1)

Takes the existing mc-router chart over from cluster-config as-is so the
deployment can move to Fleet without any change to the rolled-out state.
Convention alignment follows in stage 2, the app update in stage 3.

The only deviation from "unchanged": Chart.yaml carried name:
minecraft-server (copy-paste from the sister chart). The publish job pushes
by the glob <directory>-*.tgz while helm package names the archive after the
Chart.yaml name, so without this correction the push finds no file.

Version 0.1.1+up1.25.1 - chart semver stays at 0.1.1, the +up suffix is repo
policy and does not affect rendering.

Also wires up CI: publish workflow, change-app-version choice list,
install-test values (CI-only node-port override, since 25565 is outside the
k3d default range) and the README chart table.

ci/minecraft-router/test-values.yaml

@@ -0,0 +1,17 @@
+# minecraft-router needs no secrets, no ingress and no persistence for a CI
+# install - only two adjustments to the defaults:
+#
+# 1. server.outwardPort: the production default 25565 is outside the Kubernetes
+#    default node-port range (30000-32767). The real cluster runs an extended
+#    --service-node-port-range, the k3d CI cluster does not, so the API server
+#    would reject the Service. This is a CI-only override; the chart default
+#    stays 25565 (see minecraft-router/values.yaml).
+# 2. mappings: the chart default renders "<nil>": "<nil>:25565"; the install
+#    works either way, but the CI install uses a realistic routing table.
+server:
+  outwardPort: 30565
+mappings:
+  - domain: mc.example.com
+    internalUrl: survival-service.default.svc.cluster.local
+  - domain: creative.example.com
+    internalUrl: creative-service.default.svc.cluster.local