feat: Add skill usage tracing and tighten inventory hints

[WTW0313]

Summary

Adds the Skill Usage workflow and tightens inventory hints around related providers and Settings shortcuts.

What changed

• Added skill usage tracing/import UI, usage heatmap, provider ranking, source path display, and reset/rescan flows.
• Fixed RELATED inventory grouping so different skills from the same skills.sh repo are not treated as confirmed related providers when folder hashes are unavailable.
• Fixed the Settings footer so up/down scroll only appears when the Settings content actually overflows.
• Fixed the Usage view shift-tab handler to use Ink typed key.tab and key.shift pattern.

Root cause

• skills.sh repo provenance was previously used as a confirmed identity fallback, which was too broad for repos that publish multiple skills such as lark-* skills.
• Settings always inherited a static shortcut list, so the footer advertised scroll even when there was nothing to scroll.

Validation

• pnpm test
• pnpm build