Add MySQL 8.4 LTS and 9.x Innovation release support

[renecannao]

Task 5 of Phase 1

Plan: docs/superpowers/plans/2026-03-23-phase1-foundation-poc.md
Depends on: #1

What

• Update downloadsSettings in downloads/remote_tarballs.go to include 8.4 and 9.x versions
• Update allowedGuessVersions in downloads/guess_latest.go
• Add MySQL 8.4/9.x tarball entries to downloads/tarball_list.json (when metadata available)
• Update DbdeployerVersion in tarball_list.json
• Add test verifying new versions are recognized

Files

• Modify: downloads/remote_tarballs.go
• Modify: downloads/guess_latest.go
• Modify: downloads/tarball_list.json
• Modify: downloads/remote_registry_test.go

Notes

MySQL 8.4 is the current LTS release. 9.0/9.1/9.2 are Innovation releases. Tarball naming conventions may have changed since 8.0.x — verify actual filenames from dev.mysql.com.

Acceptance criteria

• downloadsSettings includes 8.4 and 9.x for mysql, cluster, and shell
• allowedGuessVersions includes 8.4, 9.0, 9.1, 9.2
• New test TestNewMySQLVersionsRecognized passes
• cd downloads && go test -v passes

[renecannao]

Changes included in master via stacked branch merges.