Enhance V3 CRUD: Implement Error Bubbling and Dry-Run Validation.

- Updated app/db_sql.py to capture SQL exceptions in thread-local storage for later retrieval.
- Implemented format_db_error() in app/lib_api_crud_v3.py to clean up raw MariaDB error strings.
- Added POST /v3/crud/{obj_type}/validate endpoint for dry-run payload validation.
- Updated main and nested routers to bubble up validation and database errors into the response 'meta.details' field.
- Added tests/test_v3_error_bubbling.py to verify formatting logic.

app/routers/api_crud_v3_nested.py

@@ -12,8 +12,9 @@ from app.lib_general_v3 import (
 )
 from app.lib_api_crud_v3 import (
     check_account_access, apply_forced_account_filter, filter_order_by,
-    get_supported_filters, safe_json_loads, sanitize_payload
+    get_supported_filters, safe_json_loads, sanitize_payload, format_db_error
 )
+from app.db_sql import get_last_sql_error
 from app.models.response_models import *
 from app.ae_obj_types_def import obj_type_kv_li
 
@@ -178,7 +179,7 @@ async def post_child_obj(
     try:
         validated_obj = input_model(**obj_data)
     except Exception as e:
-        return mk_resp(data=False, status_code=400, response=response, status_message=f"Validation error: {e}")
+        return mk_resp(data=False, status_code=400, response=response, status_message="Validation Failed", details=str(e))
 
     data_to_insert = validated_obj.dict(exclude_unset=True)
 
@@ -195,7 +196,8 @@ async def post_child_obj(
                 return mk_resp(data=resp_data, response=response)
         return mk_resp(data={"obj_id": new_obj_id, "obj_id_random": new_obj_id_random}, response=response)
     else:
-        return mk_resp(data=False, status_code=400, response=response, status_message="Failed to create child object.")
+        db_err = format_db_error(get_last_sql_error())
+        return mk_resp(data=False, status_code=400, response=response, status_message="Failed to create child object.", details=db_err)
 
 
 @router.get('/{parent_obj_type}/{parent_obj_id}/{child_obj_type}/{child_obj_id}', response_model=Resp_Body_Base)
@@ -286,7 +288,9 @@ async def patch_child_obj(
                 resp_data = output_model(**updated_child).dict(by_alias=serialization.by_alias, exclude_unset=serialization.exclude_unset)
                 return mk_resp(data=resp_data, response=response)
         return mk_resp(data=True, response=response, status_message="Updated successfully.")
-    return mk_resp(data=False, status_code=400, response=response, status_message="Update failed.")
+    else:
+        db_err = format_db_error(get_last_sql_error())
+        return mk_resp(data=False, status_code=400, response=response, status_message="Update failed.", details=db_err)
 
 
 @router.delete('/{parent_obj_type}/{parent_obj_id}/{child_obj_type}/{child_obj_id}', response_model=Resp_Body_Base)