Replace the onboarding AI chat feature flag with an environment variable (#23439)

Follow-up to #23199.

The AI-chat onboarding is an instance-level rollout decision, not a
per-workspace experiment, so `IS_ONBOARDING_AI_CHAT_ENABLED` becomes an
instance config variable (default `false`, editable from the admin
panel) exposed to the frontend through `ClientConfig`. The workspace
feature flag is deleted; leftover `featureFlag` rows are inert since the
column is plain text.

`IS_WORKSPACE_COMPANY_ENRICHMENT_ENABLED` is removed as redundant: the
PDL client already skips everything when no API key is set. Enrichment
now runs when the AI chat is on and `PEOPLE_DATA_LABS_API_KEY` is
configured.

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packages/twenty-front/src/modules/side-panel/components/SidePanelExpandAiChatButton.tsx

@@ -6,11 +6,10 @@ import { IconButton } from 'twenty-ui/input';
 import { useIsMobile } from 'twenty-ui/utilities';
 
 import { aiChatExpandedReturnLocationState } from '@/ai/states/aiChatExpandedReturnLocationState';
+import { isOnboardingAiChatEnabledState } from '@/client-config/states/isOnboardingAiChatEnabledState';
 import { sidePanelPageState } from '@/side-panel/states/sidePanelPageState';
 import { useAtomStateValue } from '@/ui/utilities/state/jotai/hooks/useAtomStateValue';
 import { useSetAtomState } from '@/ui/utilities/state/jotai/hooks/useSetAtomState';
-import { useIsFeatureEnabled } from '@/workspace/hooks/useIsFeatureEnabled';
-import { FeatureFlagKey } from '~/generated-metadata/graphql';
 
 export const SidePanelExpandAiChatButton = () => {
   const { t } = useLingui();
@@ -18,8 +17,8 @@ export const SidePanelExpandAiChatButton = () => {
   const location = useLocation();
   const isMobile = useIsMobile();
   const sidePanelPage = useAtomStateValue(sidePanelPageState);
-  const isOnboardingAiChatEnabled = useIsFeatureEnabled(
-    FeatureFlagKey.IS_ONBOARDING_AI_CHAT_ENABLED,
+  const isOnboardingAiChatEnabled = useAtomStateValue(
+    isOnboardingAiChatEnabledState,
   );
   const setAiChatExpandedReturnLocation = useSetAtomState(
     aiChatExpandedReturnLocationState,