feat: add Minecraft 26.3 vanilla, Paper, and Spigot scrolls

[druid-infra]

Summary

• Add Minecraft Vanilla 26.3 scrolls and build metadata.
• Add PaperMC 26.3 scrolls and build metadata.
• Add Spigot 26.3 scrolls and build metadata.
• Register all added 26.3 artifacts in scripts/push.sh.

Live version checks

• Mojang version manifest: 26.3 release; server jar verified HTTP 200.
• PaperMC Fill API: 26.3 is listed as the latest Paper family release.
• Spigot versions index: 26.3 is listed; 26.3.json reports Jenkins build 4653 and Java 25-compatible class versions.
• Forge promotions metadata: latest available promotion is 26.2 (65.1.3); no Forge 26.3 promotion or artifact is available, so Forge remains at 26.2.

Validation

• JSON metadata parsed successfully.
• New scroll YAML app versions verified as 26.3.
• bash -n scripts/push.sh passed.
• git diff --check passed.
• Go validator/tests were run where Go is available.

[druid-infra]

Error: This repo is not allowlisted for Atlantis.