Add menu bar timer showing how long Caffeine has been active

[deathemperor]

Why

The menu bar icon shows that Caffeine is active, but not for how long. For indefinite activations nothing was tracking it at all — displayTimer only ran when a timeout was set, and the menu's status item just read "Caffeine is active".

What

A live duration next to the status item icon, in monospaced digits so the item doesn't jitter as the time changes.

Three new preferences (Preferences window, below "Keep apps active"):

Preference	Key	Default
Show timer in menu bar	CAShowMenuBarTimer	on
Timer display: Elapsed / Remaining	CATimerDisplayMode	elapsed
Time format: Compact / Verbose	CATimerFormat	compact

Compact renders 0:42 / 5:07 / 1:23:45; verbose renders 42s / 5m / 1h 23m. Remaining mode has nothing to count down to for an indefinite activation, so it shows ∞ instead; elapsed mode still counts up.

Implementation notes:

• CaffeineViewModel gains activationDate and a published elapsedTime. The 1-second display timer now runs whenever Caffeine is active, not only when a timeout is set, and updates both elapsedTime and timeRemaining.
• Durations are formatted with Duration.FormatStyle, so both styles localize automatically — only the seven new preference labels needed .strings entries. They're added to all 13 localizations.
• Verbose formatting uses fractionalPart: .hide(rounded: .towardZero); without it the default rounding renders 1:23:45 as "1h 24m" and 59:59 as "60m", so the verbose readout would run ahead of the compact one.

Behavior change worth reviewing

formattedTimeRemaining() is renamed formattedStatusText() and now honors the display-mode preference. With the default elapsed mode, the menu's status item shows elapsed time for timed activations where it previously showed remaining. Happy to flip the default to remaining if you'd rather keep the existing behavior out of the box.

Testing

• xcodebuild -scheme Caffeine -destination "platform=macOS" build — succeeds.
• swiftformat . — no changes.
• All 13 Localizable.strings pass plutil -lint.
• Formatting exercised across 0s / 7s / 42s / 60s / 5m07s / 59:59 / 1h / 1h23m45s / 10h / 99:59:59 in both styles.

The 12 non-English strings are my translations and would benefit from a native-speaker pass.