3.5.0 - SQLite challenge storage

uSkyBlock 3.5.0 is a feature release that moves challenge progress into a SQLite database and modernizes placeholder support.

Challenge progress now stored in SQLite

• Challenge completion data has moved from the legacy per-player/per-island YAML files into a single SQLite database (plugins/uSkyBlock/data/challenge-progress.db), with a one-time automatic migration on first start. Includes hardening for storage integrity and legacy-migration edge cases. (#137, #146)
• Upgrade note: the migration runs once and logs a summary. Legacy entries that cannot be attached to an existing island (for example, progress belonging to players who no longer own an island) are left on disk rather than deleted, so nothing is lost.

Modernized placeholders

• Placeholder integration is now component-native, with a dedicated PlaceholderAPI module. uSkyBlock placeholders work directly inside island and party chat formats via <usb:KEY> tags. The old placeholder: config block has been removed and your config.yml migrates automatically (123 → 124). (#143)

Reliability fixes

• Harden world loading against a missing void generator. (#142)
• Fix biome permission node declarations in plugin.yml.
• Guard against null player data when clearing inventories.

Localization

• Updated translations from Crowdin. (#136)

Full Changelog: https://github.com/uskyblock/uSkyBlock/compare/v3.4.2...v3.5.0