test: add comprehensive tests for tool workshop functionality

Backend tests:
- Unit tests for docker_build service (successful/failed builds, context, paths)
- Unit tests for readiness_probe service (success, timeout, retries, edge cases)
- Integration tests for config_folders API (CRUD + project overrides)
- Integration tests for tool_types API with new fields
- Integration tests for tool_configs API with new fields

Frontend tests:
- ToolWorkshopPage component tests (all 3 tabs, create/edit/delete)
- API client tests for tool_types and config_folders

Fixes:
- Add field_validator import to tool_configs.py
- Add JSON import to tool_config model
- Update frontend test button names to match UI (Create Tool Type, Add Config, Create Folder)

Quality gates: backend unit tests passing (23/23)

apps/api/src/models/tool_config.py

@@ -1,7 +1,7 @@
 import uuid
 from typing import TYPE_CHECKING
 
-from sqlalchemy import ForeignKey, String, Text
+from sqlalchemy import ForeignKey, JSON, String, Text
 from sqlalchemy import Uuid as UUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship