Merge Map tab into Server tab and remove Map tab

The Map tab provided a form for editing world-map color thresholds
(low, medium, high). Moving this into the Server tab consolidates all
server-side configuration in one place.

- Add map color thresholds section to ServerTab with full validation
- Load map thresholds on component mount with useEffect
- Implement auto-save for threshold changes via useAutoSave hook
- Display threshold color interpolation guide
- Remove MapTab component import from ConfigPage
- Remove 'map' from TabValue type
- Remove Map tab element from TabList
- Remove conditional render for MapTab
- Remove MapTab from barrel export (index.ts)
- Delete MapTab.tsx file
- Update ConfigPage test to remove MapTab mock

All 123 frontend tests pass.

frontend/src/components/config/index.ts

@@ -34,7 +34,6 @@ export { JailFilesTab } from "./JailFilesTab";
 export { JailFileForm } from "./JailFileForm";
 export { JailsTab } from "./JailsTab";
 export { LogTab } from "./LogTab";
-export { MapTab } from "./MapTab";
 export { RawConfigSection } from "./RawConfigSection";
 export type { RawConfigSectionProps } from "./RawConfigSection";
 export { RegexList } from "./RegexList";