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.

minecraft-router/values.yaml

@@ -0,0 +1,9 @@
+server:
+  # nodePort of the router Service. 25565 is the Minecraft default port and is
+  # deliberately outside the Kubernetes default node-port range (30000-32767) -
+  # the cluster runs an extended --service-node-port-range. Do NOT "fix" this
+  # into the default range: the Minecraft clients connect to this exact port.
+  outwardPort: 25565
+mappings:
+  - domain: null
+    internalUrl: null