feat: add Minecraft Forge 26.3 scroll

[druid-infra]

Summary

• Add the missing Minecraft Forge 26.3 scroll.
• Register the Forge 26.3 artifact and Java 25 runtime metadata.
• Add Forge 26.3 runtime, update, packet-handler, and server configuration files.

Upstream checks

• Mojang version manifest: latest release 26.3.
• Forge promotions: 26.3-latest is 66.0.6.
• Spigot API Maven metadata: latest 26.3-R0.1-SNAPSHOT.
• The repository already contains Vanilla, PaperMC, and Spigot 26.3 scrolls; Forge was the missing family/version.

Validation

• git diff --check passes.
• go test ./... and ./scripts/validate_all_scrolls.sh could not run because Go is not installed in the environment.

[druid-infra]

Error: This repo is not allowlisted for Atlantis.