Weather refetch gets skipped when watch has no data

[mattrossman]

On some dev installs the watchface starts on No data :( and stays there until I open settings and force a weather refetch.

The mismatch seems to be:

• the watch UI decides whether weather exists from persisted C-side state (forecast_start)
• PKJS decides whether to auto-fetch only from phone-side localStorage (lastFetchSuccess)

So the phone can think weather is still fresh while the watch has no valid forecast data, and startup/tick fetches get skipped.

Smallest fix idea:

• have the watch send a startup ping saying whether it has valid forecast data
• if not, PKJS should force a fetch immediately
• keep the current 30-minute freshness gate when the watch already has data

Relevant code:

• src/c/layers/loading_layer.c:36-42
• src/pkjs/index.js:558-586
• src/c/appendix/app_message.c:127-135

[mattrossman]

Fixed in #128