Redesign watchface with countdown bar and calendar support

- Force 24h time format; switch date to DD/MM (Gothic 28 Bold)
- Replace effect-layer invert with explicit black background + white text
- Add 8px top bar counting down to next :00/:30; preempts to nearest
  calendar appointment when one arrives via AppMessage within 30 min
- Add pkjs with Google Calendar API integration (falls back gracefully
  if no API key is configured)
- Move battery indicator to a 4px full-width strip at screen bottom
- Drop pebble-effect-layer dependency; add APPOINTMENT_MINUTES messageKey
- Write README with feature overview, build instructions, and calendar setup

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

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+# Countdown Watchface
+
+A clean Pebble watchface with a top progress bar that counts down to your next half-hour mark or upcoming calendar appointment.
+
+## Features
+
+- **Time** — large 24-hour format (`HH:MM`) using the Roboto Bold 49 font
+- **Date** — day/month number (`DD/MM`) in Gothic 28 Bold below the time
+- **Countdown bar** — 8px bar across the top of the screen:
+  - Starts full at the top of each half hour and drains to empty as it approaches `:00` or `:30`
+  - If a calendar appointment is within the next 30 minutes, the bar counts down to that instead
+  - Requires Google Calendar API setup (see below); falls back to half-hour countdown without it
+- **Battery bar** — thin 4px indicator along the bottom edge
+
+## Supported platforms
+
+`aplite`, `basalt`, `diorite`, `emery`, `flint`
+
+## Building
+
+Requires the [Pebble SDK](https://developer.rebble.io/developer.pebble.com/sdk/index.html) (version 3).
+
+```bash
+cd countdown_watchface
+pebble build
+```
+
+Install on a connected watch or emulator:
+
+```bash
+pebble install --phone <watch-ip>
+# or
+pebble install --emulator basalt
+```
+
+## Calendar integration (optional)
+
+The watchface uses Google Calendar API to detect appointments within the next 30 minutes. Without this, the bar simply counts down to the next `:00` or `:30`.
+
+**Setup:**
+
+1. Create a Google Cloud project and enable the **Google Calendar API**.
+2. Generate an **API key** (restrict it to the Calendar API and your IP/app if desired).
+3. In the Pebble phone app's JS console (or via a config page), run:
+
+```javascript
+localStorage.setItem('gcal_api_key', 'YOUR_API_KEY_HERE');
+```
+
+The calendar ID defaults to `primary`. To use a different calendar, edit `src/pkjs/index.js` and change the `CALENDAR_ID` variable.
+
+The phone-side JS polls for events every minute and sends the minutes-to-appointment to the watch via AppMessage. If the API call fails or no key is set, the watch falls back to the half-hour countdown automatically.