fix(ai-tools): make navigate_app tool schema a valid object root for direct model binding (#22284)

## Problem

Using an AI Agent step in a workflow fails with:

> Invalid schema for function 'navigate_app': schema must be a JSON
Schema of 'type: "object"', got 'type: "None"'.

## Root cause

The `navigate_app` tool declared its `inputSchema` as a top-level
`z.discriminatedUnion('type', [...])`. When serialized via
`toToolJsonSchema`, a discriminated union produces a **root-level
`anyOf`** with no top-level `"type"`:

```json
{ "anyOf": [ { "type": "object", ... }, ... ] }

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packages/twenty-server/src/engine/core-modules/tool/tools/navigate-tool/navigate-app-tool.schema.ts

@@ -1,6 +1,6 @@
 import { z } from 'zod';
 
-export const NavigateAppInputZodSchema = z.discriminatedUnion('type', [
+export const NavigateAppActionZodSchema = z.discriminatedUnion('type', [
   z.object({
     type: z
       .literal('navigateToView')
@@ -59,4 +59,11 @@ export const NavigateAppInputZodSchema = z.discriminatedUnion('type', [
   }),
 ]);
 
+export const NavigateAppInputZodSchema = z.object({
+  navigation: NavigateAppActionZodSchema.describe(
+    'The navigation action to perform.',
+  ),
+});
+
+export type NavigateAppAction = z.infer<typeof NavigateAppActionZodSchema>;
 export type NavigateAppInput = z.infer<typeof NavigateAppInputZodSchema>;

packages/twenty-server/src/engine/core-modules/tool/tools/navigate-tool/navigate-app-tool.ts

@@ -54,7 +54,7 @@ export class NavigateAppTool implements Tool {
       };
     }
 
-    const input: NavigateAppInput = parseResult.data;
+    const input: NavigateAppInput['navigation'] = parseResult.data.navigation;
 
     switch (input.type) {
       case 'navigateToView':