Fix freebuff model tab navigation

[jahooma]

Summary

• Normalize freebuff model selector navigation keys so Tab advances and Shift+Tab moves backward like arrow keys.
• Stop propagation after selector navigation so handled Tab events stay scoped to the model picker.
• Add unit coverage for arrow, Tab, Shift+Tab, Kitty Tab, and modifyOtherKeys Shift+Tab inputs.

Tests

• bun test cli/src/utils/tests/freebuff-model-navigation.test.ts
• bun run --cwd cli typecheck