Merge Global tab into Server tab and remove Global tab

Global tab provided the same four editable fields as Server tab:
log_level, log_target, db_purge_age, db_max_matches. Server tab already
has these fields plus additional read-only info (db_path, syslog_socket)
and a Flush Logs button.

- Add hint text to DB Purge Age and DB Max Matches fields in ServerTab
- Remove GlobalTab component import from ConfigPage
- Remove 'global' from TabValue type
- Remove Global tab element from TabList
- Remove conditional render for GlobalTab
- Remove GlobalTab from barrel export (index.ts)
- Delete GlobalTab.tsx file
- Update ConfigPage test to remove Global tab test case

All 123 frontend tests pass.

frontend/src/components/config/index.ts

@@ -30,7 +30,6 @@ export { ExportTab } from "./ExportTab";
 export { FilterForm } from "./FilterForm";
 export type { FilterFormProps } from "./FilterForm";
 export { FiltersTab } from "./FiltersTab";
-export { GlobalTab } from "./GlobalTab";
 export { JailFilesTab } from "./JailFilesTab";
 export { JailFileForm } from "./JailFileForm";
 export { JailsTab } from "./JailsTab";