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/pages/__tests__/ConfigPage.test.tsx

@@ -9,7 +9,6 @@ vi.mock("../../components/config", () => ({
   JailsTab: () => <div data-testid="jails-tab">JailsTab</div>,
   FiltersTab: () => <div data-testid="filters-tab">FiltersTab</div>,
   ActionsTab: () => <div data-testid="actions-tab">ActionsTab</div>,
-  GlobalTab: () => <div data-testid="global-tab">GlobalTab</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>,
@@ -45,12 +44,6 @@ describe("ConfigPage", () => {
     expect(screen.getByTestId("actions-tab")).toBeInTheDocument();
   });
 
-  it("switches to Global tab when Global tab is clicked", () => {
-    renderPage();
-    fireEvent.click(screen.getByRole("tab", { name: /global/i }));
-    expect(screen.getByTestId("global-tab")).toBeInTheDocument();
-  });
-
   it("switches to Server tab when Server tab is clicked", () => {
     renderPage();
     fireEvent.click(screen.getByRole("tab", { name: /server/i }));