fix(recipes): make batch-import directory browser work on Windows (#1106)

The browse endpoint and its frontend were written with POSIX-only
assumptions, so on Windows pressing Browse immediately failed with
"Access denied to this directory":

- The frontend opened the browser at "/", which resolves to the
  current drive root on Windows.
- The allowlist check used Path("/"), which has no drive letter on
  Windows, so relative_to() rejected every drive-qualified path —
  anything outside the user profile was denied.

Fixes:
- Empty browse path now defaults to the user home directory instead of
  erroring; the frontend sends "" rather than the POSIX-only "/".
- The access check is platform-aware (drive-qualified on Windows,
  absolute on POSIX).
- Parent navigation uses the server-provided parent_path; the root
  check is now path.parent == path (the old str/anchor comparison
  self-looped at Windows drive roots).
- Browsing up from a Windows drive root shows a virtual list of
  available drives so users can switch drives without typing a path.

tests/routes/test_batch_import_browse_directory.py

@@ -0,0 +1,97 @@
+import json
+import logging
+import os
+from pathlib import Path
+
+import pytest
+
+from py.routes.handlers.recipe_handlers import BatchImportHandler
+
+
+def _make_handler() -> BatchImportHandler:
+    return BatchImportHandler(
+        ensure_dependencies_ready=None,  # browse_directory never calls it
+        recipe_scanner_getter=lambda: None,
+        civitai_client_getter=lambda: None,
+        logger=logging.getLogger(__name__),
+        batch_import_service=None,
+    )
+
+
+class _Request:
+    def __init__(self, path: str) -> None:
+        self._path = path
+
+    async def json(self):
+        return {"path": self._path}
+
+
+async def _browse(handler: BatchImportHandler, path: str):
+    response = await handler.browse_directory(_Request(path))
+    return response, json.loads(response.text)
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_lists_subdirs_and_images(tmp_path):
+    (tmp_path / "subdir").mkdir()
+    (tmp_path / "photo.png").write_bytes(b"x")
+    (tmp_path / "notes.txt").write_text("not an image")
+
+    response, payload = await _browse(_make_handler(), str(tmp_path))
+
+    assert response.status == 200
+    assert payload["success"] is True
+    assert payload["current_path"] == str(tmp_path)
+    assert [d["name"] for d in payload["directories"]] == ["subdir"]
+    assert [f["name"] for f in payload["image_files"]] == ["photo.png"]
+    assert payload["parent_path"] == str(tmp_path.parent)
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_empty_path_defaults_to_home(tmp_path, monkeypatch):
+    # The frontend no longer sends the POSIX-only "/" as the initial path; an
+    # empty path must resolve to the user's home directory (#1106).
+    monkeypatch.setattr(Path, "home", lambda: tmp_path)
+
+    response, payload = await _browse(_make_handler(), "")
+
+    assert response.status == 200
+    assert payload["success"] is True
+    assert payload["current_path"] == str(tmp_path)
+
+
+@pytest.mark.skipif(os.name == "nt", reason="POSIX root semantics")
+@pytest.mark.asyncio
+async def test_browse_directory_root_has_no_parent():
+    _, payload = await _browse(_make_handler(), os.path.abspath(os.sep))
+
+    assert payload["success"] is True
+    assert payload["parent_path"] is None
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_windows_drives_token(monkeypatch):
+    # The token branch returns before any pathlib use, so faking os.name is
+    # enough to exercise it on POSIX (#1106).
+    monkeypatch.setattr(os, "name", "nt")
+    monkeypatch.setattr(os, "listdrives", lambda: ["C:\\", "D:\\"], raising=False)
+
+    response, payload = await _browse(
+        _make_handler(), BatchImportHandler.WINDOWS_DRIVES_TOKEN
+    )
+
+    assert response.status == 200
+    assert payload["success"] is True
+    assert payload["current_path"] == ""
+    assert payload["parent_path"] is None
+    assert [d["name"] for d in payload["directories"]] == ["C:\\", "D:\\"]
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_missing_directory_returns_404(tmp_path):
+    response, payload = await _browse(
+        _make_handler(), str(tmp_path / "does-not-exist")
+    )
+
+    assert response.status == 404
+    assert payload["success"] is False