windows: fix XDG-related test failures on Windows

Make the "cache directory paths" test cross-platform by using
std.fs.path.join for expected values and a platform-appropriate
mock home path, since the function under test uses native path
separators.

Skip the two shell integration XDG_DATA_DIRS tests on Windows.
These tests use hardcoded Unix path separators (:) and Unix default
paths (/usr/local/share:/usr/share) which are not applicable on
Windows where the path delimiter is ; and XDG_DATA_DIRS is not a
standard concept.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/os/xdg.zig

@@ -132,7 +132,7 @@ test {
 test "cache directory paths" {
     const testing = std.testing;
     const alloc = testing.allocator;
-    const mock_home = "/Users/test";
+    const mock_home = if (builtin.os.tag == .windows) "C:\\Users\\test" else "/Users/test";
 
     // Test when XDG_CACHE_HOME is not set
     {
@@ -140,7 +140,9 @@ test "cache directory paths" {
         {
             const cache_path = try cache(alloc, .{ .home = mock_home });
             defer alloc.free(cache_path);
-            try testing.expectEqualStrings("/Users/test/.cache", cache_path);
+            const expected = try std.fs.path.join(alloc, &.{ mock_home, ".cache" });
+            defer alloc.free(expected);
+            try testing.expectEqualStrings(expected, cache_path);
         }
 
         // Test with subdir
@@ -150,7 +152,9 @@ test "cache directory paths" {
                 .subdir = "ghostty",
             });
             defer alloc.free(cache_path);
-            try testing.expectEqualStrings("/Users/test/.cache/ghostty", cache_path);
+            const expected = try std.fs.path.join(alloc, &.{ mock_home, ".cache", "ghostty" });
+            defer alloc.free(expected);
+            try testing.expectEqualStrings(expected, cache_path);
         }
     }
 }

src/termio/shell_integration.zig

@@ -670,6 +670,8 @@ fn setupXdgDataDirs(
 }
 
 test "xdg: empty XDG_DATA_DIRS" {
+    if (builtin.os.tag == .windows) return error.SkipZigTest;
+
     const testing = std.testing;
 
     var arena = ArenaAllocator.init(testing.allocator);
@@ -696,6 +698,8 @@ test "xdg: empty XDG_DATA_DIRS" {
 }
 
 test "xdg: existing XDG_DATA_DIRS" {
+    if (builtin.os.tag == .windows) return error.SkipZigTest;
+
     const testing = std.testing;
 
     var arena = ArenaAllocator.init(testing.allocator);