Adiciona start.bat do servidor Paper 1.21.8 e corrige inicializacao

[oTalentz]

Summary

Cria server/start.bat para iniciar o servidor Paper 1.21.8 diretamente no Windows, garantindo o uso do jar oficial paper-1.21.8-60.jar. O batch:

• Verifica se o Java 21 esta instalado.
• Baixa o paper-1.21.8-60.jar caso nao exista.
• Baixa os plugins de dependencia (ViaVersion, ViaBackwards, LuckPerms, Vault) para server/plugins/.
• Cria eula.txt automaticamente.
• Reinicia o servidor em caso de queda.

Tambem corrige a deteccao de plugins em start.sh (o glob estava dentro de aspas e nunca encontrava os jars existentes, forcando rebuild toda vez) e ajusta server/docker-compose.yml para baixar o ViaBackwards pelo Modrinth, porque o download via Spiget (27448) estava falhando.

server/.gitignore foi ampliado para ignorar os arquivos de runtime gerados pelo Paper (worlds, logs, configs, cache, libraries, e dados dentro de plugins/).

Testes

• ./start.sh subiu o container e o servidor iniciou com todos os plugins: Coins, Tags, LuckPerms, Vault, ViaVersion, ViaBackwards.
• java -jar paper-1.21.8-60.jar iniciou localmente com o mesmo conjunto de plugins funcionando.

Link to Devin session: https://app.devin.ai/sessions/e69d8057169b4c75bd8424a5269051a4
Requested by: @oTalentz

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