Preset system: Add set-priority command and info display

[mbachorik]

Summary

Add preset set-priority command and priority display in preset info for consistency with extension system.

Context

After adding priority-based resolution to extensions (#1845), presets lacked:

• specify preset set-priority command to change priority after installation
• Priority display in specify preset info output

Changes

• Add preset set-priority <pack-id> <priority> command
• Show priority in preset info output for installed presets
• Add backwards compatibility tests for legacy presets without priority field

Related

• Companion to Extension system: Add priority-based resolution ordering #1845 (extension priority support)
• Ensures parity between preset and extension systems