Add Dashboard menu bar display mode

[mvelluet]

Summary

• Adds a new Dashboard display mode in the menu bar settings (between Timer and All)
• Shows both session and weekly quotas with their respective countdowns: 76% · 2h31m | 9% · 5j
• Session timer uses hours+minutes (2h31m) or minutes+seconds (14m30s)
• Weekly timer uses the largest meaningful unit only (5j, 23h, 58m, 30s) to stay compact
• Uses 1-second refresh interval for live countdown (same as Timer mode)

Changes

• MenuBarDisplayMode: new fullDashboard case (position 3, before allQuotas)
• UsageManager: added sessionQuota / weeklyQuota computed properties and timeUntilSessionReset / timeUntilWeeklyReset published properties
• compactTimeString(): static helper that formats a TimeInterval as the largest unit (days → hours → minutes → seconds)
• updateCountdown(): calculates both per-quota timers when in Dashboard mode
• setupCountdownTimer(): enables fast (1s) timer for Dashboard mode

Example display

C 76% · 2h31m | 9% · 5j

[mvelluet]