test: fix 3 CI failures for cross-platform test compatibility

- test_get_token_from_keychain_windows_branch: Also mock is_macos() to False
  to prevent macOS CI from calling macOS keychain before checking mocked
  is_windows flag

- test_find_git_from_bash_path_env_var: Mock Path.exists to return False
  to prevent Windows CI from finding actual Git installation at
  C:\Program Files\Git\bin\bash.exe, ensuring test falls through to
  shutil.which as expected

- test_hash_with_makefile: Add 10ms delay between file writes to ensure
  different mtime on CI systems with coarse modification time resolution

tests/core/test_auth.py

@@ -1120,9 +1120,10 @@ class TestGetTokenFromKeychainPlatformBranches:
         assert result == "sk-ant-oat01-macos-token"
         mock_macos_keychain.assert_called_once_with(None)
 
+    @patch("core.auth.is_macos", return_value=False)
     @patch("core.auth.is_windows", return_value=True)
     @patch("core.auth._get_token_from_windows_credential_files")
-    def test_get_token_from_keychain_windows_branch(self, mock__get_token_from_windows_credential_files, mock_is_windows):
+    def test_get_token_from_keychain_windows_branch(self, mock__get_token_from_windows_credential_files, mock_is_windows, mock_is_macos):
         """Test get_token_from_keychain calls Windows implementation"""
         # Arrange
         mock__get_token_from_windows_credential_files.return_value = "sk-ant-oat01-windows-token"

tests/core/test_git_executable.py

@@ -108,13 +108,15 @@ class TestFindGitExecutable:
         bash_path = "C:\\Program Files\\Git\\bin\\bash.exe"
 
         with patch.dict(os.environ, {"CLAUDE_CODE_GIT_BASH_PATH": bash_path}, clear=False):
-            # When bash path is set but git is not found, it falls through to shutil.which
-            with patch("shutil.which", return_value="/usr/bin/git"):
-                # Act
-                result = _find_git_executable()
+            # Mock Path.exists to return False so bash path check fails
+            # This ensures we fall through to shutil.which
+            with patch("pathlib.Path.exists", return_value=False):
+                with patch("shutil.which", return_value="/usr/bin/git"):
+                    # Act
+                    result = _find_git_executable()
 
-                # Assert - should find git from shutil.which
-                assert result == "/usr/bin/git"
+                    # Assert - should find git from shutil.which
+                    assert result == "/usr/bin/git"
 
     def test_find_git_from_bash_path_bin_git(self):
         """Test finding git.exe in bin/ directory from bash path"""

tests/project/test_project_analyzer.py

@@ -286,11 +286,16 @@ class TestComputeProjectHash:
 
     def test_hash_with_makefile(self, temp_project_dir: Path):
         """Test hash computation with Makefile."""
+        import time
+
         (temp_project_dir / "Makefile").write_text("build:\n\techo building")
 
         analyzer = ProjectAnalyzer(temp_project_dir)
         hash1 = analyzer.compute_project_hash()
 
+        # Small delay to ensure different mtime on systems with coarse mtime resolution
+        time.sleep(0.01)
+
         # Modify Makefile
         (temp_project_dir / "Makefile").write_text("build:\n\techo modified")