fix(grid-display): restore Maidenhead grid square in DE/DX panels

[ceotjoe]

Summary

• Fixes blank Maidenhead grid squares in both the DE and DX location panels
• Root cause: commit d1ab3d5 (PR Issue951 maidenhead grid to utils geo #964) replaced calculateGridSquare(lat, lon) with latLonToMaidenhead but kept the old two-positional-argument call style — latLonToMaidenhead expects a { lat, lon } object as its first argument
• Passing a bare number caused destructuring to yield undefined for both lat and lon, producing NaN throughout the calculation and invisible characters in the rendered grid

Change

src/hooks/app/useTimeState.js lines 101-102:

Before (broken): latLonToMaidenhead(configLocation.lat, configLocation.lon)
After (correct): latLonToMaidenhead(configLocation)

Both configLocation and dxLocation are already { lat, lon } objects, so they can be passed directly.

Test plan

• Open the app and confirm the DE panel shows a 6-character Maidenhead locator (e.g. GH52lj)
• Confirm the DX panel also shows a locator
• Set a DX location manually and confirm the locator updates
• Verify a station at lat=0 / lon=0 (equator / prime meridian) renders JJ00aa — not blank

🤖 Generated with Claude Code

[alanhargreaves]

Looks good to me. I don't see any other instances.

[MichaelWheeley]

added #982 for meridian / anti-meridian unit tests, and fix for special case longitude = +180