File storage cleaning (#18381)

- Remove feature flag
- Remove legacy methods in file-upload and file-service
- Migrate AI Chat to new file management

---------

Co-authored-by: Charles Bochet <charles@twenty.com>

packages/twenty-front/src/modules/ai/utils/mapDBPartToUIMessagePart.ts

@@ -1,5 +1,8 @@
 import { type ReasoningUIPart, type ToolUIPart } from 'ai';
-import { type ExtendedUIMessagePart } from 'twenty-shared/ai';
+import {
+  type ExtendedFileUIPart,
+  type ExtendedUIMessagePart,
+} from 'twenty-shared/ai';
 import { type AgentMessagePart } from '~/generated-metadata/graphql';
 
 export const mapDBPartToUIMessagePart = (
@@ -23,7 +26,8 @@ export const mapDBPartToUIMessagePart = (
         mediaType: part.fileMediaType!,
         filename: part.fileFilename!,
         url: part.fileUrl!,
-      };
+        fileId: part.fileId!,
+      } as ExtendedFileUIPart;
     case 'source-url':
       return {
         type: 'source-url',