fix(windows): read .graphify_root BOM-tolerantly in the update-recovery path too (#3028)

Complete the read-side BOM fix: the graphify update (no-args) recovery path at cli.py read
.graphify_root with plain utf-8, so a PowerShell-written BOM would fail the exists() check
and abort with path not found. Switch it to utf-8-sig like the other five reader sites.
Also clean up two invalid-escape f-strings in the windows skillgen test.

graphify/cli.py

@@ -2274,7 +2274,11 @@ def dispatch_command(cmd: str) -> None:
             # Try to recover the scan root saved by the last full build
             saved = Path(_GRAPHIFY_OUT) / ".graphify_root"
             if saved.exists():
-                watch_path = Path(saved.read_text(encoding="utf-8").strip())
+                # utf-8-sig: a marker written by Windows PowerShell 5.1 carries a
+                # UTF-8 BOM that plain utf-8 keeps as U+FEFF (not stripped by
+                # .strip()), which would make this recovered path fail exists()
+                # (#3028). Match the other .graphify_root readers.
+                watch_path = Path(saved.read_text(encoding="utf-8-sig").strip())
             else:
                 watch_path = Path(".")
         if not watch_path.exists():

tests/test_skillgen.py

@@ -1107,10 +1107,10 @@ def test_windows_skill_writes_marker_files_without_a_bom():
     """
     core, _ = _platform_artifacts("windows")
     for marker in (".graphify_python", ".graphify_root"):
-        assert f"Out-File -FilePath graphify-out\{marker} -Encoding utf8" not in core, (
+        assert f"Out-File -FilePath graphify-out\\{marker} -Encoding utf8" not in core, (
             f"the windows render still writes {marker} with a BOM-emitting Out-File"
         )
-        assert f"WriteAllText((Join-Path $PWD 'graphify-out\{marker}')" in core, (
+        assert f"WriteAllText((Join-Path $PWD 'graphify-out\\{marker}')" in core, (
             f"{marker} must be written through WriteAllText with a BOM-less encoding"
         )
     assert "New-Object System.Text.UTF8Encoding $false" in core, \