Bring minecraft-server up to the chart style guidelines (1.0.0+upjava8)

Stage 2 of the Fleet migration for minecraft-server. Major bump: runtime
behaviour changes (probes, hardening) and the values interface breaks
(resource renames, strict schema).

Two real bugs first:
- The container declared port 35565 while the Service targeted 25565. It
  only worked because targetPort was numeric. Both are now server.port
  (25565) and the Service targets the named port.
- The download-serverpack init container was guarded by the map
  .Values.curseforgeServerpack instead of .enabled, so it rendered for
  every release and silently no-opped on an empty wget URL.

Conventions:
- Resources renamed to <release>-<chart>-<kind>, templates to
  <app>.<kind>.yaml. The PVC deliberately keeps its historical name -
  renaming it would provision a new, empty volume and orphan the worlds.
- Probes (liveness/readiness/startup) via the image's own mc-health, so
  Ready means the server answers a server-list ping. Startup budget 20 min.
- Hardened, values-configurable security contexts: non-root uid 1000,
  read-only root filesystem with an emptyDir at /tmp, all caps dropped.
- Resources from values with the limitFactor helper; an unset memory
  request is derived from the JVM heap so the two cannot drift apart.
- Additive env block rendered through tpl, pinned init image, storage
  class as a value, RCON wiring only when actually enabled.
- curseforge/ftb/curseforgeServerpack are now mutually exclusive.
- minecraft.version is pinned to the Java line instead of LATEST.
- The mc-router auto-discovery annotation is gone; the service type it
  implicitly switched is now the explicit value server.service.type.

Schema pilot (#68): values.schema.json with additionalProperties false on
every chart-owned level, rejecting all three known dead keys.

minecraft-server/Chart.yaml

@@ -1,24 +1,15 @@
 apiVersion: v2
 name: minecraft-server
 description: A Helm chart for deploying a itzg/minecraft-server
+icon: https://avatars.githubusercontent.com/u/988985
 
-# A chart can be either an 'application' or a 'library' chart.
-#
-# Application charts are a collection of templates that can be packaged into versioned archives
-# to be deployed.
-#
-# Library charts provide useful utilities or functions for the chart developer. They're included as
-# a dependency of application charts to inject those utilities and functions into the rendering
-# pipeline. Library charts do not define any templates and therefore cannot be deployed.
 type: application
 
-# This is the chart version. This version number should be incremented each time you make changes
-# to the chart and its templates, including the app version.
-# Versions are expected to follow Semantic Versioning (https://semver.org/)
-version: 0.4.0+upjava21
+# The Java line of this chart version is chosen through appVersion, which is
+# the image tag: the chart is published once per line (java8 / java17 / java21)
+# and minecraft.version in values.yaml must match the line published here.
+version: 1.0.0+upjava8
+appVersion: "java8"
 
-# This is the version number of the application being deployed. This version number should be
-# incremented each time you make changes to the application. Versions are not expected to
-# follow Semantic Versioning. They should reflect the version the application is using.
-# It is recommended to use it with quotes.
-appVersion: "java21"
+maintainers:
+  - name: jklein