fix(frontend): show validation errors when agent type form fails

When form validation fails (e.g., personality_prompt is empty), the form
would silently not submit. Now it shows a toast with the first error
and navigates to the tab containing the error field.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/agents/AgentTypeForm.tsx

@@ -7,9 +7,10 @@
 
 'use client';
 
-import { useEffect, useState } from 'react';
-import { useForm, Controller } from 'react-hook-form';
+import { useEffect, useState, useCallback } from 'react';
+import { useForm, Controller, type FieldErrors } from 'react-hook-form';
 import { zodResolver } from '@hookform/resolvers/zod';
+import { toast } from 'sonner';
 import { Button } from '@/components/ui/button';
 import { Input } from '@/components/ui/input';
 import { Textarea } from '@/components/ui/textarea';
@@ -89,6 +90,30 @@ export function AgentTypeForm({
     formState: { errors },
   } = form;
 
+  // Handle form validation errors - show toast with first error
+  const handleFormError = useCallback((formErrors: FieldErrors<AgentTypeCreateFormValues>) => {
+    // Find the first error and show it
+    const firstErrorKey = Object.keys(formErrors)[0] as keyof AgentTypeCreateFormValues;
+    if (firstErrorKey) {
+      const error = formErrors[firstErrorKey];
+      const message = error && 'message' in error ? error.message : 'Validation error';
+      toast.error('Please fix form errors', {
+        description: `${String(firstErrorKey)}: ${message}`,
+      });
+
+      // Navigate to the tab containing the error
+      if (['name', 'slug', 'description', 'expertise', 'is_active'].includes(firstErrorKey)) {
+        setActiveTab('basic');
+      } else if (['primary_model', 'fallback_models', 'model_params'].includes(firstErrorKey)) {
+        setActiveTab('model');
+      } else if (['mcp_servers', 'tool_permissions'].includes(firstErrorKey)) {
+        setActiveTab('permissions');
+      } else if (firstErrorKey === 'personality_prompt') {
+        setActiveTab('personality');
+      }
+    }
+  }, []);
+
   const watchName = watch('name');
   /* istanbul ignore next -- defensive fallback, expertise always has default */
   const watchExpertise = watch('expertise') || [];
@@ -133,7 +158,7 @@ export function AgentTypeForm({
   };
 
   return (
-    <form onSubmit={handleSubmit(onSubmit)} className={className}>
+    <form onSubmit={handleSubmit(onSubmit, handleFormError)} className={className}>
       {/* Header */}
       <div className="mb-6 flex items-center gap-4">
         <Button type="button" variant="ghost" size="icon" onClick={onCancel}>