Add configurable map defaults with admin Settings page

[Knobee]

Summary

• New Settings page under Admin nav with interactive map preview for configuring default lat/lon, zoom, and map layer
• Click the map to set coordinates, scroll to zoom, dropdown switches tile layer — all bidirectionally synced with form fields
• Map tab now loads position from: localStorage (returning user) > admin config via GET /api/config > hardcoded fallbacks
• Saves user's map position and layer to localStorage on pan/zoom/layer change
• Graceful degradation: if backend doesn't have /api/config endpoint (old version), falls back to hardcoded defaults with no errors

Backward compatibility

• Old UI + New backend: no breakage, map uses hardcoded defaults
• New UI + Old backend: GET /api/config returns 404, map falls back to hardcoded defaults, Settings page shows version mismatch message

Test plan

• Admin > Settings page loads with current defaults
• Click map to set lat/lon — fields update
• Scroll to zoom — zoom field updates without recentering
• Change layer dropdown — map preview switches tile source
• Save settings — verify success notification
• Map tab opens at configured position and layer
• Pan/zoom on Map tab, navigate away and back — remembers position (localStorage)
• Incognito window — uses admin defaults (no localStorage)
• Header username menu renders above the map (z-index)

Companion backend PR: brian7704/OpenTAKServer#284
Fixes #165

🤖 Generated with Claude Code