## Summary
This PR migrates the SMHI weather provider from the deprecated PMP3gv2
API to the new SNOW1gv1 API.
The old API (pmp3g/version/2) started returning HTTP 404 on 2026-03-31.
## Changes
- Updated API endpoint:
- `pmp3g/version/2` → `snow1g/version/1`
- Updated response parsing:
- `validTime` → `time`
- `parameters[]` → `data` (flat structure)
- Updated parameter names:
- `t` → `air_temperature`
- `ws` → `wind_speed`
- etc.
- Updated precipitation handling to match new
`predominant_precipitation_type_at_surface`
- Updated coordinate parsing (flat `[lon, lat]`)
- Added missing value handling (`9999 → null`)
## Notes
- Maintains backward compatibility for `precipitationValue` config
- No UI changes
- Symbol mapping unchanged (same codes 1–27)
## Testing
- Verified against live SMHI SNOW1gv1 API responses
- Confirmed old API returns HTTP 404
## Impact
Fixes broken SMHI provider due to API deprecation.
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