refactor: remove Tool Configs and Config Folders

These features are fully superseded by Config Profiles which provide:
- Env vars, file mounts, port overrides, start commands, working dirs
- Git mounts, profile composition, cycle detection
- Default selection, project/tool-type scoping

Changes:
- Delete backend models: ToolConfig, ConfigFolder
- Delete backend APIs: tool_configs.py, config_folders.py
- Delete frontend API clients: tool_configs.ts, config_folders.ts
- Remove Tool Config fetching from start_instance, use ConfigProfile only
- Simplify merge_with_config to accept only profile (no tool_configs)
- Remove configs/folders tabs from Tool Workshop page
- Delete associated integration and unit tests
- Add Alembic migration to drop tool_configs and config_folders tables

Quality gates: backend tests 59 passed, frontend typecheck clean

apps/api/src/models/__init__.py

@@ -1,5 +1,4 @@
 from src.models.base import Base
-from src.models.config_folder import ConfigFolder
 from src.models.config_profile import ConfigProfile, ConfigProfileInclude
 from src.models.git_repository import GitRepository
 from src.models.project import Project
@@ -13,7 +12,6 @@ from src.models.user_config import UserConfig
 
 __all__ = [
     "Base",
-    "ConfigFolder",
     "ConfigProfile",
     "ConfigProfileInclude",
     "GitRepository",