feat: forward TimelinePin reminders to the timeline emulator

[kchinnasamy]

Summary

PebbleKit2 1.2.0 added an optional reminders list to TimelinePin
(pebble-dev/PebbleKitAndroid2#14),
but PebbleSenderReceiver.toPinJson() dropped the field when converting to
TimelinePinJson — so a reminder attached to a PebbleKit2 pin never reached
RemoteTimelineEmulator, and the watch never buzzed.

This maps reminders through (each TimelineReminder → TimelineReminderJson,
reusing a small shared TimelineLayout.toLayoutJson() helper) and bumps
pebblekit2 1.1.0 → 1.2.0 so the new field is on the classpath.
RemoteTimelineEmulator.insertPin already reads pin.reminders and inserts the
matching reminder rows, so nothing changes there.

Why

A TimelinePin inserted via PebbleKit2's insertTimelinePin is otherwise
silent — there's no way for a third-party app (e.g. a companion that schedules
reminders) to make the watch buzz at the pin's time. This closes that gap on the
host side.

Notes

• The pebblekit2 bump is in the root version catalog, so it applies app-wide.
  1.2.0 is backward compatible — it only adds the optional reminders field.
• Same change as feat: forward TimelinePin reminders to the timeline emulator matejdro/libpebble3#4 (microPebble lineage), where
  :libpebble3:compileDebugKotlinAndroid is green. The patch is identical and
  the touched libpebble3 source is shared, so this is verified on that side.

Test plan

• End-to-end: third-party PebbleKit2 app inserts a pin carrying a reminder → watch buzzes at reminder time

Backward compatible: pins without reminders serialize exactly as before
(reminders is omitted when empty).