Refresh forecast up to 3× per day within daylight window

forecast.solar updates estimates as the day progresses, so a single
morning fetch can be stale by afternoon. New behaviour:
- Re-fetch every 4h within 07:00–19:00 window (3 fetches/day)
- Outside the window always serve the cached value
- Free tier limit is 12 req/day — 3 fetches is well within budget
- First startup outside window still fetches if cache is empty

Config: forecast.fetch_interval, fetch_window_start, fetch_window_end

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

configs/ems-config.yaml

@@ -95,6 +95,9 @@ forecast:
   declination: 20           # panel tilt in degrees
   azimuth: 5                # degrees from south (south=0, west=90, east=-90)
   kwp: 7.0                  # installed peak power
+  fetch_interval: "4h"      # re-fetch during the day (free tier: 12 req/day → 3 fetches)
+  fetch_window_start: "07:00"
+  fetch_window_end: "19:00"
 
 # EMS operational settings
 ems: