Flatten AI tool call output structure (#19524)

## Summary
Refactored the `AgentChatMessageUIToolCallPart` output structure to
flatten the nested result object, simplifying the data model and
improving code clarity.

## Key Changes
- **Flattened output structure**: Moved `success`, `message`, and
`result` fields from `output.result` directly to `output`, eliminating
unnecessary nesting
- **Removed `toolName` field**: Deleted the unused `toolName` property
from the output object
- **Made fields optional**: Changed `error` and `result` to optional
fields to better represent cases where they may not be present
- **Updated hook logic**: Modified `useProcessUIToolCallMessage` to
access the flattened structure:
- Changed `toolExecutionPart.output.result.success` to
`toolExecutionPart.output.success`
- Changed `toolExecutionPart.output.result.result` to
`toolExecutionPart.output.result`
- Added null check for `navigateAppOutput` to handle cases where result
is undefined

## Implementation Details
The refactoring maintains backward compatibility in functionality while
simplifying the data structure. The optional `result` field now properly
reflects that navigation output may not always be present, with an
explicit guard clause added to handle this case gracefully.

https://claude.ai/code/session_01EnYKwVaCJyhgNPsi7p3YSq

Co-authored-by: Claude <noreply@anthropic.com>

packages/twenty-front/src/modules/ai/hooks/useProcessUIToolCallMessage.ts

@@ -42,7 +42,7 @@ export const useProcessUIToolCallMessage = () => {
         continue;
       }
 
-      if (toolExecutionPart.output.result.success !== true) {
+      if (toolExecutionPart.output.success !== true) {
         continue;
       }
 
@@ -51,7 +51,11 @@ export const useProcessUIToolCallMessage = () => {
         toolExecutionPart.toolCallId,
       ]);
 
-      const navigateAppOutput = toolExecutionPart.output.result.result;
+      const navigateAppOutput = toolExecutionPart.output.result;
+
+      if (!isDefined(navigateAppOutput)) {
+        continue;
+      }
 
       switch (navigateAppOutput.action) {
         case 'navigateToObject': {