test: dep-check probe command must exist on Windows too

python3 is not a command on a stock Windows install; caught by the new
windows-latest CI job. Probe 'python' there and accept warn (found on
augmented PATH) as proof of resolution.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/test_core.py

@@ -227,8 +227,11 @@ def test_diagnostics_redacts_token_args():
 # --------------------------------------------------------------------------- #
 # 6. Dependency / PATH checking
 # --------------------------------------------------------------------------- #
-def test_dep_check_finds_python3():
-    assert c.check_dependency({"command": "python3"})["status"] == "ok"
+def test_dep_check_finds_python():
+    # "python3" does not exist on a stock Windows install; "warn" (found only
+    # on an augmented PATH) still proves resolution works on a real machine.
+    cmd = "python" if os.name == "nt" else "python3"
+    assert c.check_dependency({"command": cmd})["status"] in ("ok", "warn")
 
 
 def test_dep_check_flags_missing():