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These features are fully superseded by Config Profiles which provide: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/main.py

@@ -15,9 +15,7 @@ from src.api.projects import router as projects_router
 from src.api.ssh_keys import router as ssh_keys_router
 from src.api.terminal import router as terminal_router
 from src.api.instance_proxy import router as instance_proxy_router
-from src.api.config_folders import router as config_folders_router
 from src.api.config_profiles import router as config_profiles_router
-from src.api.tool_configs import router as tool_configs_router
 from src.api.tool_definitions import router as tool_definitions_router
 from src.api.tool_instances import router as tool_instances_router
 from src.api.tool_instances import sessions_router
@@ -130,10 +128,8 @@ app.include_router(git_repositories_router)
 app.include_router(user_config_router)
 app.include_router(tool_types_router)
 app.include_router(tool_definitions_router)
-app.include_router(config_folders_router)
 app.include_router(config_profiles_router)
 app.include_router(tool_instances_router)
-app.include_router(tool_configs_router)
 app.include_router(sessions_router)
 app.include_router(instance_proxy_router)
 app.include_router(terminal_router)