fix(canary): friendly "manifest not found" instead of a raw OS error

Live smoke: `soup data canary check --manifest nope.json` surfaced
"[WinError 2] Не удается найти указанный файл: 'nope.json'" -- a raw,
locale-dependent OS error leaking straight through from os.path.getsize,
where every other Soup command says "File not found: <path>".

src/soup_cli/utils/canary.py

@@ -166,6 +166,10 @@ def _harden_permissions(path: str) -> None:
 def load_manifest(path: str) -> tuple[Canary, ...]:
     """Read a canary manifest written by :func:`write_manifest`."""
     safe = enforce_under_cwd_and_no_symlink(str(path), "manifest")
+    if not os.path.isfile(safe):
+        # Without this the caller surfaces a raw (locale-dependent) OS error
+        # from getsize — e.g. "[WinError 2] Не удается найти указанный файл".
+        raise ValueError(f"manifest not found: {path}")
     if os.path.getsize(safe) > _MAX_MANIFEST_BYTES:
         raise ValueError(
             f"manifest too large (max {_MAX_MANIFEST_BYTES} bytes)"

tests/test_v07136.py

@@ -1430,6 +1430,18 @@ class TestCanaryManifest:
                 generate_canaries(count=1, seed=0), str(tmp_path / "esc.json")
             )
 
+    def test_missing_manifest_is_a_friendly_message(self, tmp_path, monkeypatch):
+        """Not a raw locale-dependent OS error.
+
+        Live smoke surfaced "[WinError 2] Не удается найти указанный файл"
+        leaking straight through from os.path.getsize.
+        """
+        from soup_cli.utils.canary import load_manifest
+
+        monkeypatch.chdir(tmp_path)
+        with pytest.raises(ValueError, match="manifest not found"):
+            load_manifest("nope.json")
+
     def test_malformed_manifest_rejected(self, tmp_path, monkeypatch):
         from pathlib import Path