feat(settings): directory picker and live validation for path settings

Add a reusable directory-picker modal backed by a new generic
POST /api/lm/browse-directory endpoint (browse logic extracted from the
recipe batch-import handler into py/utils/directory_browser.py) and wire
a browse button plus advisory validate-path feedback (POST
/api/lm/validate-path) into the settings path inputs: recipes path,
example images path/local root, and the extra-folder/model-path rows.

The browse button insets into the right edge of static inputs so narrow
settings rows keep their single-control layout.

Translations for the new settings.directoryPicker and
settings.pathValidation keys are filled in for all 9 locales.

tests/routes/test_filesystem_paths.py

@@ -0,0 +1,183 @@
+import json
+import os
+from pathlib import Path
+from types import SimpleNamespace
+
+import pytest
+
+from py.routes.handlers.misc_handlers import FileSystemHandler
+
+
+def _make_handler() -> FileSystemHandler:
+    # browse_directory/validate_path never touch the settings service
+    return FileSystemHandler(settings_service=SimpleNamespace())
+
+
+class _Request:
+    def __init__(self, body: dict) -> None:
+        self._body = body
+
+    async def json(self):
+        return self._body
+
+
+async def _browse(handler: FileSystemHandler, path: str):
+    response = await handler.browse_directory(_Request({"path": path}))
+    return response, json.loads(response.text)
+
+
+async def _validate(handler: FileSystemHandler, path: str, expect: str = "directory"):
+    response = await handler.validate_path(
+        _Request({"path": path, "expect": expect})
+    )
+    return response, json.loads(response.text)
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_empty_path_defaults_to_home(tmp_path, monkeypatch):
+    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.asyncio
+async def test_browse_directory_lists_subdirs_sorted_and_filters(tmp_path):
+    (tmp_path / "zeta").mkdir()
+    (tmp_path / "alpha").mkdir()
+    (tmp_path / ".hidden").mkdir()
+    (tmp_path / "node_modules").mkdir()
+    (tmp_path / "__pycache__").mkdir()
+
+    response, payload = await _browse(_make_handler(), str(tmp_path))
+
+    assert response.status == 200
+    assert payload["success"] is True
+    assert [d["name"] for d in payload["directories"]] == ["alpha", "zeta"]
+    assert payload["directory_count"] == 2
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_missing_returns_404(tmp_path):
+    response, payload = await _browse(_make_handler(), str(tmp_path / "nope"))
+
+    assert response.status == 404
+    assert payload["success"] is False
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_file_path_returns_400(tmp_path):
+    file_path = tmp_path / "file.txt"
+    file_path.write_text("x")
+
+    response, payload = await _browse(_make_handler(), str(file_path))
+
+    assert response.status == 400
+    assert payload["success"] is False
+
+
+@pytest.mark.asyncio
+async def test_browse_directory_relative_path_returns_403(monkeypatch):
+    # resolve() normally absolutizes relative paths against the cwd; bypass it
+    # to exercise the access-denied branch directly.
+    monkeypatch.setattr(Path, "resolve", lambda self: self)
+
+    response, payload = await _browse(_make_handler(), "relative/path")
+
+    assert response.status == 403
+    assert payload["success"] is False
+
+
+@pytest.mark.asyncio
+async def test_validate_path_existing_directory(tmp_path):
+    response, payload = await _validate(_make_handler(), str(tmp_path))
+
+    assert response.status == 200
+    assert payload == {
+        "success": True,
+        "path": os.path.abspath(str(tmp_path)),
+        "exists": True,
+        "is_directory": True,
+        "readable": True,
+        "writable": True,
+        "error_code": None,
+    }
+
+
+@pytest.mark.asyncio
+async def test_validate_path_not_found(tmp_path):
+    response, payload = await _validate(_make_handler(), str(tmp_path / "missing"))
+
+    assert response.status == 200
+    assert payload["success"] is True
+    assert payload["exists"] is False
+    assert payload["error_code"] == "path_not_found"
+
+
+@pytest.mark.asyncio
+async def test_validate_path_file_when_directory_expected(tmp_path):
+    file_path = tmp_path / "file.txt"
+    file_path.write_text("x")
+
+    response, payload = await _validate(_make_handler(), str(file_path))
+
+    assert response.status == 200
+    assert payload["error_code"] == "not_a_directory"
+    assert payload["exists"] is True
+    assert payload["is_directory"] is False
+
+
+@pytest.mark.asyncio
+async def test_validate_path_expect_file_on_file(tmp_path):
+    file_path = tmp_path / "file.txt"
+    file_path.write_text("x")
+
+    response, payload = await _validate(_make_handler(), str(file_path), expect="file")
+
+    assert response.status == 200
+    assert payload["error_code"] is None
+    assert payload["exists"] is True
+    assert payload["is_directory"] is False
+
+
+@pytest.mark.skipif(
+    not hasattr(os, "geteuid") or os.geteuid() == 0,
+    reason="root bypasses permission checks",
+)
+@pytest.mark.asyncio
+async def test_validate_path_unreadable_directory(tmp_path):
+    locked = tmp_path / "locked"
+    locked.mkdir()
+    locked.chmod(0o000)
+    try:
+        response, payload = await _validate(_make_handler(), str(locked))
+    finally:
+        locked.chmod(0o755)
+
+    assert response.status == 200
+    assert payload["error_code"] == "not_readable"
+    assert payload["readable"] is False
+
+
+@pytest.mark.asyncio
+async def test_validate_path_empty_path_returns_400():
+    response, payload = await _validate(_make_handler(), "")
+
+    assert response.status == 400
+    assert payload["success"] is False
+
+
+@pytest.mark.asyncio
+async def test_validate_path_expands_user(tmp_path, monkeypatch):
+    subdir = tmp_path / "subdir"
+    subdir.mkdir()
+    monkeypatch.setenv("HOME", str(tmp_path))
+
+    response, payload = await _validate(_make_handler(), "~/subdir")
+
+    assert response.status == 200
+    assert payload["error_code"] is None
+    assert payload["path"] == os.path.abspath(str(subdir))