fix(issue): Replace stopwatch toggle with explicit start/stop actions (#34818)

This PR fixes a state de-synchronization bug with the issue stopwatch,
it resolves the issue by replacing the ambiguous `/toggle` endpoint
with two explicit endpoints: `/start` and `/stop`.

- The "Start timer" button now exclusively calls the `/start` endpoint.
- The "Stop timer" button now exclusively calls the `/stop` endpoint.

This ensures the user's intent is clearly communicated to the server,
eliminating the state inconsistency and fixing the bug.

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

options/locale/locale_en-US.ini

@@ -1726,6 +1726,8 @@ issues.remove_time_estimate_at = removed time estimate %s
 issues.time_estimate_invalid = Time estimate format is invalid
 issues.start_tracking_history = started working %s
 issues.tracker_auto_close = Timer will be stopped automatically when this issue gets closed
+issues.stopwatch_already_stopped = The timer for this issue is already stopped
+issues.stopwatch_already_created = The timer for this issue already exists
 issues.tracking_already_started = `You have already started time tracking on <a href="%s">another issue</a>!`
 issues.stop_tracking = Stop Timer
 issues.stop_tracking_history = worked for <b>%[1]s</b> %[2]s