fix: support Gitea 28.0.0 mail templates

.github/release-notes/v28.0.0.md

@@ -0,0 +1,21 @@
+FEATURES
+
+- COMPATIBILITY
+    - Add a Gitea 28.0.0-aligned release of all 10 themes and 11 mail types per theme
+
+BUGFIXES
+
+- THEMES (All 10)
+    - Replace the removed `FileSize` function with `FormatByteSize` in release-attachment emails, preventing Gitea 28.0.0 template rendering errors
+- PREVIEW AND TESTS
+    - Match the preview's file-size function to Gitea 28.0.0 and render release attachments in the example data
+    - Add an all-theme regression test for release attachments and the removed function
+
+DOCS
+
+- Update the English and Simplified Chinese READMEs and compatibility matrix for Gitea 28.0.0
+- Clarify that v28.0.0 requires Gitea 28.0.0; use v1.27.3 for Gitea 1.25.0–1.27.3
+
+---
+
+**Full Changelog:** [v1.27.3...v28.0.0](https://github.com/KenanZhu/GiteaMailTemplates/compare/v1.27.3...v28.0.0)