chore: drop the A6 rollback tombstones

A6 deployed cleanly and the provider keys are gone from the production `.env`,
which makes the legacy collector inert regardless of any settings row. The two
tombstones migration 029 pinned have no remaining job, and nothing in the
codebase reads either key.

Migration 030 deletes them and drops the Admin filter that hid them. Unlike
029's, its downgrade is meaningful — it restores both rows at their safe values,
since going back past this revision means going back toward code that reads them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/components/admin/SettingsForm.tsx

@@ -3,14 +3,6 @@ import { useSettings, useUpdateSetting } from '../../hooks/useAdmin';
 import { SkeletonTable } from '../ui/Skeleton';
 import type { SystemSetting } from '../../lib/types';
 
-// Retired keys kept in the database as rollback tombstones (migration 029).
-// They no longer control anything; hide them so nobody edits a dead switch.
-// Delete both the rows and this filter once the A6 rollback window has closed.
-const MANAGED_SETTINGS = new Set([
-  'fundamental_data_sec_dolt_cutover_enabled',
-  'job_fundamental_collector_enabled',
-]);
-
 export function SettingsForm() {
   const { data: settings, isLoading, isError, error } = useSettings();
   const updateSetting = useUpdateSetting();
@@ -40,11 +32,10 @@ export function SettingsForm() {
   if (isLoading) return <SkeletonTable rows={4} cols={2} />;
   if (isError) return <p className="text-sm text-red-400">{(error as Error)?.message || 'Failed to load settings'}</p>;
   if (!settings || settings.length === 0) return <p className="text-sm text-gray-500">No settings found.</p>;
-  const visibleSettings = settings.filter((setting) => !MANAGED_SETTINGS.has(setting.key));
 
   return (
     <div className="space-y-4">
-      {visibleSettings.map((setting) => (
+      {settings.map((setting) => (
         <div key={setting.key} className="glass p-4 flex flex-wrap items-center gap-3 glass-hover">
           <label className="min-w-[140px] text-sm font-medium text-gray-300">{setting.key}</label>
           {setting.key === 'registration' ? (