fix: datetime serialization in API response models

Tool types and git repositories response models declared created_at/
updated_at as str but ORM returns datetime objects. Change to datetime
type so Pydantic serializes correctly to ISO format strings.

apps/api/src/api/git_repositories.py

@@ -2,6 +2,7 @@ import os
 import shutil
 import subprocess
 import uuid
+from datetime import datetime
 
 from fastapi import APIRouter, Depends, HTTPException, Response, status
 from pydantic import BaseModel, ConfigDict
@@ -57,8 +58,9 @@ class GitRepositoryResponse(BaseModel):
     owner_id: uuid.UUID
     is_mirror: bool
     remote_url: str | None
-    last_push: str | None
+    last_push: datetime | None
-    created_at: str | None
+    created_at: datetime
+    updated_at: datetime
 
 
 @router.post("/{project_id}/repositories", response_model=GitRepositoryResponse, status_code=status.HTTP_201_CREATED)

apps/api/src/api/tool_types.py

@@ -1,4 +1,5 @@
 import uuid
+from datetime import datetime
 
 import yaml
 from fastapi import APIRouter, Depends, HTTPException, status
@@ -112,8 +113,8 @@ class ToolTypeResponse(BaseModel):
     required_variables: list[str]
     is_builtin: bool
     created_by_id: uuid.UUID | None
-    created_at: str
+    created_at: datetime
-    updated_at: str
+    updated_at: datetime
 
 
 @router.post("", response_model=ToolTypeResponse, status_code=status.HTTP_201_CREATED)