feat(web): Claude limit-window usage progress bars in sidebar panel footer (todo 2524)

Surface the cached 'y claude usage' scrape (session/week_all/week_sonnet %)
as color-coded horizontal bars in the ~280px left sidebar panel footer.

- storage: vm_config.claude_usage JSONB cache + repo/service get/save_claude_usage
- cli: 'y claude usage' write-through (best-effort, UTC scraped_at, never breaks scrape)
- api: GET /api/claude/usage pure DB read (vm_name optional->default, blob or cached:false, id-free)
- web: ClaudeUsageWidget (SWR 60s, color bars, reset+as-of tooltip, stale/no-data states)
  mounted as persistent sidebar panel footer (option A placement)