Add paid pomodoro breaks

Some jobs pay for breaks, so a pomodoro break shouldn't take time off
the workday. By default (new setting `paid_breaks`, in [reminders]), b
on the Tracker, zb anywhere or :break starts a pomodoro break WITHOUT
pausing the shift: the break stays in your worked time and the data
file isn't touched. b (or s) brings you back to focus. With the setting
off, b pauses the shift like p. p and e always stop the clock.

For the rhythm, a paid break still counts as a break: reminders::PaidBreaks
keeps them in memory and pomodoro() cuts them out of the focus stretches,
the same way as a pause. Stopping the shift ends a paid break, and
closing the work day forgets them.

The Tracker shows "on a paid break" and the paid break's progress, and
the nudges name the right key (b or p/s).

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/action.rs

@@ -41,6 +41,9 @@ pub enum Action {
         since: Timestamp,
         stopped: Option<Timestamp>,
     },
+    /// Start a pomodoro break, or come back from one. With paid breaks the
+    /// shift keeps running; without, it's the same as Pause / Start.
+    TakeBreak,
     /// Silence the break suggestion for a while.
     Snooze,