update checking for mods, resource packs, shaders, and other

[objz]

what would you like

Support update checks and controlled updates for every provider-managed content type.

completed

• cached background checks for the complete content manifest
• Update badges for installed mods, resource packs, shaders, and managed modpacks
• u bulk updates for mods, resource packs, and shaders
• per-world datapack updates from the open world
• one conflict list after scanning and dependency resolution
• current-to-target review before installing
• one staged content transaction with rollback on failure
• managed modpack updates with user-file preservation and rollback
• v version selection for individual content, including reinstalling the current version

Explicit modpack reinstall and arbitrary version selection remain tracked in #37 because they use the same refresh engine but need their own instance-list controls.

[objz]

implemented in #31: complete cached checks, atomic bulk content updates, per-world datapack updates, and rollback-safe managed modpack updates. explicit modpack reinstall/version controls remain in #37.