feat: add AI chat error handling for billing and API key errors (#16797)

## Summary

This PR adds user-friendly error handling for AI chat features,
specifically for **billing credits exhausted** and **API key not
configured** errors.

## Changes

### Backend
- Added `BILLING_CREDITS_EXHAUSTED` exception code with 402 status
- Added `API_KEY_NOT_CONFIGURED` exception code with 503 status
- Added billing check before AI chat streaming in
`agent-chat.controller.ts`
- Added error code to HTTP exception response body for frontend error
type detection
- Created `AgentRestApiExceptionFilter` for agent-specific errors

### Frontend
- Created `AIChatBanner` - reusable banner component for error/warning
messages
- Created `AIChatCreditsExhaustedMessage` - shows upgrade prompts based
on user permissions
- Created `AIChatApiKeyNotConfiguredMessage` - shows configuration
guidance with docs link
- Created `AIChatErrorRenderer` - encapsulates error type switching
logic (fixes nested ternary)
- Created `AIChatStandaloneError` - displays errors when there are no
messages
- Split `aiChatErrorUtils.ts` into separate files (1 export per file):
  - `AIChatErrorCode.ts`
  - `extractErrorCode.ts`
  - `isAIChatErrorOfType.ts`
  - `isBillingCreditsExhaustedError.ts`
  - `isApiKeyNotConfiguredError.ts`
- Added comprehensive test coverage (27 tests)

### Other
- Updated trial period banner messaging

## Testing
- All lint checks pass
- All 27 new tests pass
- TypeScript typecheck passes

packages/twenty-server/src/engine/core-modules/exception-handler/http-exception-handler.service.ts

@@ -21,11 +21,11 @@ import {
   TwentyORMExceptionCode,
 } from 'src/engine/twenty-orm/exceptions/twenty-orm.exception';
 import { handleException } from 'src/engine/utils/global-exception-handler.util';
+import { CustomException } from 'src/utils/custom-exception';
 
 interface RequestAndParams {
   request: Request | null;
-  // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  params: any;
+  params: Record<string, string | undefined>;
 }
 
 const getErrorNameFromStatusCode = (statusCode: number) => {
@@ -34,6 +34,8 @@ const getErrorNameFromStatusCode = (statusCode: number) => {
       return 'BadRequestException';
     case 401:
       return 'UnauthorizedException';
+    case 402:
+      return 'PaymentRequiredException';
     case 403:
       return 'ForbiddenException';
     case 404:
@@ -66,13 +68,11 @@ export class HttpExceptionHandlerService {
 
   handleError = (
     exception: Error | HttpException,
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    response: Response<any, Record<string, any>>,
+    response: Response,
     errorCode?: number,
     user?: ExceptionHandlerUser,
     workspace?: ExceptionHandlerWorkspace,
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-  ): Response<any, Record<string, any>> | undefined => {
+  ): Response | undefined => {
     const params = this.request?.params;
 
     if (params?.workspaceId) {
@@ -121,6 +121,7 @@ export class HttpExceptionHandlerService {
       statusCode,
       error: exception.name ?? getErrorNameFromStatusCode(statusCode),
       messages: [exception?.message],
+      code: exception instanceof CustomException ? exception.code : undefined,
     });
   };
 }