fix(compose): remove server.properties-aliased env vars so UI edits persist

The itzg/minecraft-bedrock-server entrypoint rewrites server.properties
from env vars on every start. Any property edited via mc-manager's UI was
being clobbered because those env vars were set here. Remove them so
/data/server.properties (on the named volume) is the real source of truth:

  - SERVER_NAME, GAMEMODE, DIFFICULTY, ALLOW_CHEATS, ONLINE_MODE,
    MAX_PLAYERS, DEFAULT_PLAYER_PERMISSION_LEVEL
  - LEVEL_SEED (jamie) — world already generated
  - LEVEL_NAME — moved to docker-compose.override.yml, managed by
    mc-manager so UI Set Active survives future deploys

Kept: EULA, SERVER_PORT (deploy-time wiring), OP_PERMISSION_LEVEL
(not a server.properties key).

Override file is gitignored so mc-manager's writes don't leak into git.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -16,6 +16,10 @@ addon/build/
 # Environment
 .env
 
+# docker-compose override, managed by mc-manager at runtime for per-service state
+# (LEVEL_NAME, etc.) that must survive deploys. Never committed.
+docker-compose.override.yml
+
 # Server data (Docker volumes are external, but just in case)
 server-data/