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/pages/__tests__/ConfigPage.test.tsx

@@ -10,7 +10,6 @@ vi.mock("../../components/config", () => ({
   FiltersTab: () => <div data-testid="filters-tab">FiltersTab</div>,
   ActionsTab: () => <div data-testid="actions-tab">ActionsTab</div>,
   ServerTab: () => <div data-testid="server-tab">ServerTab</div>,
-  MapTab: () => <div data-testid="map-tab">MapTab</div>,
   RegexTesterTab: () => <div data-testid="regex-tab">RegexTesterTab</div>,
   ExportTab: () => <div data-testid="export-tab">ExportTab</div>,
 }));