style: ruff check --fix on Phase C files

CI's QA → Python Isolation → Lint failed on two issues:

1. workspace_files.py:45 had quoted forward refs ('docker.types.Mount')
   when the underlying type is runtime-imported inside the method —
   ruff RUF066 prefers unquoted when possible. Now uses 'from docker
   import types as docker_types' at module level and references the
   real type without quotes.

2. tests/test_workspace_files.py imported pytest unnecessarily
   (F401). Tests use plain functions, not pytest fixtures from the
   import.

Auto-fixed via 'uv run ruff check --fix .'. 174 tests still pass.

Author: NeuralEmpowerment

lib/python/agentic_isolation/agentic_isolation/workspace_files.py

@@ -35,14 +35,14 @@ class WorkspaceFiles:
     client — callers pass in whatever client they're already using.
     """
 
-    client: "docker.DockerClient"
+    client: docker.DockerClient
 
     def bind_mount(
         self,
         host_path: Path,
         container_path: str,
         read_only: bool = True,
-    ) -> "docker.types.Mount":
+    ) -> docker.types.Mount:
         """Build a Mount descriptor for `containers.create(mounts=[...])`.
 
         Relative host_paths are resolved to absolute paths (Docker rejects

lib/python/agentic_isolation/tests/test_workspace_files.py

@@ -6,8 +6,6 @@
 from pathlib import Path
 from unittest.mock import MagicMock
 
-import pytest
-
 
 def test_bind_mount_descriptor_shape(tmp_path: Path):
     """bind_mount() returns a docker.types.Mount with the expected