* Add multi-day calendar selection with custom popover UI
Replace native DatePicker with a custom-themed CalendarPopover supporting
non-contiguous multi-day selection. Add --days CLI flag for comma-separated
date filtering that post-filters from the bounding range scan.
CLI: parseDaysFlag() parses and validates dates, filterProjectsByDays()
filters turns to only selected days. Verified that sum of individual --day
calls matches --days output across cost, calls, activities, models, and
providers.
Swift: DataClient passes --days for multi-day, with single-day fallback.
AppStore tracks selectedDays as Set<String> with PayloadCacheKey support.
CalendarPopover uses pending state committed only on Done tap.
* Clear + Done in calendar resets to current period
When user clears all selected days and taps Done, switch back to the
active period instead of silently keeping the old day selection.
- Fix refresh loop: proper while loop with 30s sleep and force:true
instead of single-fire Task that never repeated
- Fix loading overlay: counter-based isLoading so concurrent fetches
don't flicker the overlay on/off
- Fix rapid tab switching: cancel previous switchTask, check
Task.isCancelled after CLI returns to discard stale results
- Fix tab strip vs hero desync: fetch provider-specific and all-provider
data in parallel so costs arrive from same data snapshot
- Fix stale menubar icon after wake: forceRefresh now fetches today/all
in parallel alongside the current selection
- Fix accent color: ThemeState is now @Observable so color changes
propagate via observation, removing .id() view hierarchy teardown
- Fix currency flash: defer store.currency and symbol update until a
rate is available so symbol and rate apply atomically
- Fix export: terminationHandler instead of waitUntilExit (no UI freeze),
HHmmss in filename to prevent overwrite on double-export
- Fix CurrencyState: @MainActor isolation with proper Sendable
conformance, nonisolated on pure static functions
- Fix streak count: iterate calendar days instead of sparse history
entries so gaps are counted as streak-breakers
- Fix TrendBar identity: stable date-based id instead of UUID
- Add GPT-5.3 and DeepSeek model display names
