Pin minecraft-server to dated image tags and fix the whitelist switch (2.0.0+up2026.8.2.java8)

Stage 3 of the Fleet migration. Two changes, both breaking, hence the major
bump from 1.0.0 to 2.0.0.

Dated image tags: appVersion moves from the rolling line tag "java8" to the
immutable upstream release tag "2026.8.2-java8". The rolling tags are rebuilt
continuously, so a pod restart could pull a different image than the previous
start without that being recorded anywhere. 2026.8.2 is the newest upstream
release (published 2026-08-23) and exists for all three Java lines.

Whitelist semantics: the chart now wires ENABLE_WHITELIST (and ENFORCE_WHITELIST)
in both positions, so minecraft.whitelist.enabled: false actually switches the
whitelist off. Previously the chart only emitted whitelist variables while
enabled was true and had no way to express "off" - and because server.properties
lives on the PVC, a release that had once written white-list=true kept it
forever. players stays guarded by enabled, since a non-empty WHITELIST enables
the whitelist in the image regardless of ENABLE_WHITELIST.

The default flips from enabled: true to enabled: false. Under the corrected
semantics the old default (enabled with an empty player list) would mean a
server nobody can join; false matches both the image and vanilla Minecraft.

minecraft-server/values.schema.json

@@ -156,13 +156,16 @@
           "additionalProperties": false,
           "properties": {
             "enabled": {
+              "description": "Wired to the image's ENABLE_WHITELIST in both positions: true sets white-list=true (and enforce-whitelist=true), false rewrites white-list=false into an existing server.properties on the volume. true without players locks everyone out - that is the image's semantics and it is intended.",
               "type": "boolean"
             },
             "overridePolicy": {
+              "description": "EXISTING_WHITELIST_FILE - how an already existing whitelist.json is treated. Only applies while enabled is true.",
               "type": "string",
               "enum": ["SKIP", "MERGE", "SYNCHRONIZE"]
             },
             "players": {
+              "description": "Comma-separated players, passed as WHITELIST only while enabled is true (a non-empty WHITELIST would otherwise enable the whitelist despite ENABLE_WHITELIST=false).",
               "type": ["string", "null"]
             }
           }