fix: support Gitea 28.0.0 mail templates

AGENTS.md

@@ -35,7 +35,7 @@ docs/               # Bilingual documentation (English + Simplified Chinese)
 
 ### Template Files
 - All `.tmpl` files use Go `html/template` syntax
-- Must use only Gitea's built-in template functions: `AppUrl`, `DotEscape`, `QueryEscape`, `ShortSha`, `HTMLFormat`, `PathEscapeSegments`, `FileSize`
+- Must use only Gitea 28's built-in template functions: `AppUrl`, `DotEscape`, `QueryEscape`, `ShortSha`, `HTMLFormat`, `PathEscapeSegments`, `FormatByteSize`
 - Must use only official Gitea translation keys (`mail.*` namespace)
 - Never reference `.DisplayName` in templates where the data context lacks it (collaborator, transfer, release, workflow_run, assigned, default)
 - Each style must have all 11 template types
@@ -67,7 +67,7 @@ docs/               # Bilingual documentation (English + Simplified Chinese)
 ## Versioning
 
 - Release tags identify actual downloadable packages; the compatibility matrix distinguishes released tags from source-only fixes
-- The current release is **v1.27.3**, verified against Gitea 1.27.3; it fixes the push-notification bug in Bloom, Ember, and Heritage that affects v1.27.2 on Gitea 1.27.1+. The quick-reference table in `COMPATIBILITY.md` lists the active release first; the tracker workflow updates that row by position
+- The current release is **v28.0.0**, verified against Gitea 28.0.0. Gitea 28 removes `FileSize` in favor of `FormatByteSize`, so v28.0.0 is not compatible with Gitea 1.25.0–1.27.3; use v1.27.3 for those versions. The quick-reference table in `COMPATIBILITY.md` lists the active release first; the tracker workflow updates that row by position
 - When a new Gitea version is checked: update the top `COMPATIBILITY.md` row and README badge; keep unreleased fixes distinct from the published release, and update verified/tested wording only after verification
 - Tag a new release (`vX.Y.Z`) only when the template content itself changes — the release workflow packages automatically on tag push
 - Before tagging, add `.github/release-notes/vX.Y.Z.md`; the release workflow validates the file, runs `go test ./...`, and publishes those reviewed notes with the archives