Fix untouched geofence saves on mobile

[justcallmekoko]

Summary

• render fully unconfigured geofence slots with empty label/latitude/longitude/radius values across browsers
• validate radius only when any field in a slot is supplied
• reject missing, non-numeric, or out-of-range configured radii before mutating any settings
• preserve the existing 0.10-1.00 mile rule and configured geofence round-tripping

Diagnosis

The page serialized each default radius as 0.00 while also setting HTML min=0.10. Mobile browsers retain that numeric value and fail native constraint validation before POST, even when the slot is untouched. The POST handler also treated every emitted latitude field as a configured slot and silently clamped radius. The fix normalizes a fully untouched slot to empty form values and gates server validation on whether any field is provided.

Validation

• python -m unittest discover -s tools -p test_*.py (10 passed)
• git diff --check
• ESP32-C5 compile and artifact steps passed in Actions run 30829916777

The repository has no web-portal test harness, so device/browser verification should use this regression matrix:

1. Mobile browser, all five geofences untouched: submit succeeds and other settings remain saveable.
2. Desktop browser, all five geofences untouched: submit continues to succeed.
3. Existing configured geofence: values render and round-trip unchanged.
4. Cleared configured geofence: all four blank fields save the canonical unconfigured record.
5. Partial slot (label, latitude, or longitude supplied) with blank radius: client/server reject it.
6. Configured radius below 0.10, above 1.00, or non-numeric via direct POST: server returns HTTP 400 before saving any settings.
7. Configured radius at 0.10 and 1.00: submit succeeds.