Mirror the combined multi-device dashboard in the macOS menubar via a
Local/Combined scope toggle (Settings -> Display). Builds on the menubar-json
`--scope combined` contract.
- MenubarScope enum (.local default) persisted in UserDefaults; PayloadCacheKey
gains a scope dimension so local and combined payloads cache separately.
- DataClient.fetch(scope:): a pure statusSubcommand builder appends
`--scope combined` only for combined, forces `--provider all` (the CLI rejects
combined with a provider/project/exclude filter), and coerces multi-day
selections to local (the CLI rejects combined + --days).
- MenubarPayload decodes the optional `combined` block (per-device + totals);
nil when absent (back-compat).
- The badge always stays on the local payload; the combined network pull lives
on a separate cache key and falls back to local with a "Combined unavailable"
indicator, so a slow/offline peer never blocks the badge.
- Hero shows combined totals + a per-device breakdown in Combined scope; the
token metric stays input+output (cache excluded) to match local; the
per-device daily-budget warning is suppressed for a multi-device total;
selecting Combined resets the provider tab to All.
Tests run via `swift test` (CommandLineTools Testing.framework on the rpath, no
Xcode): scope persistence, argv (local/combined/provider-forcing/multi-day),
cache-key partition, badge-survives-combined-failure, combined decode, token
consistency, provider reset, budget suppression.
