fix(worldclock): leave a fitting margin and drop the zone-cache reset

The fitted seconds size keeps five percent spare, since hinted glyph
advances do not scale exactly. The receiver no longer resets the
process's default zone: that was speculative, and it changed global
state from a UI flow. The settings state takes the seconds flag without
a default, and a garbled KDoc sentence is fixed.

docs/ARCHITECTURE.md

@@ -2464,9 +2464,7 @@ arrive with the tab on screen (a network zone change on landing, split
 screen). So `ClockChanges` (`AndroidClockChanges`, a receiver registered only
 while the tab collects) restarts the tick: those two make the state re-read
 the clock and the zone at once, and the restarted ticker measures its next
-wait against the clock as it now reads. On `TIMEZONE_CHANGED` the receiver
-also resets the process's cached default zone itself, since the system's own
-reset is a separate call that can land after the broadcast. The signal is combined
+wait against the clock as it now reads. The signal is combined
 with the stored list, the home zone and the setting *outside* the
 `flatMapLatest`, so the receiver is registered once per subscription, not
 once per list edit. Each broadcast costs one extra `build`, which