fix: prevent double translation of already-translated Docker paths

Added check in translate_path_for_environment() to detect and skip
already-translated container paths (those starting with /workspace).

This prevents the function from attempting to translate paths like:
- /workspace/src/main.py -> /inaccessible/outside/mounted/volume/workspace/src/main.py

Now it correctly handles:
- Host path: /Users/.../src/main.py -> /workspace/src/main.py (translation)
- Container path: /workspace/src/main.py -> /workspace/src/main.py (no change)

Added comprehensive test to verify double-translation prevention.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

utils/file_utils.py

@@ -195,6 +195,11 @@ def translate_path_for_environment(path_str: str) -> str:
         # Not in the configured Docker environment, no translation needed
         return path_str
 
+    # Check if the path is already a container path (starts with /workspace)
+    if path_str.startswith(str(CONTAINER_WORKSPACE) + "/") or path_str == str(CONTAINER_WORKSPACE):
+        # Path is already translated to container format, return as-is
+        return path_str
+
     try:
         # Use os.path.realpath for security - it resolves symlinks completely
         # This prevents symlink attacks that could escape the workspace