feat: Add avatar stacks (#37594)

Parse `Co-authored-by:` trailers from commit messages and surface
contributors as an avatar stack across the commit page, commits list, PR
commits tab, latest-commit row, blame, graph, and dashboard feed.

- Up to 10 visible 20px avatars, GitHub-style overlap (6px first stride,
4px between subsequent), `+N` chip for the rest.
- Label: 1 → name; 2 → `<a> and <b>`; 3+ → `<N> people` opens a Tippy
popup with all participants.
- Names and avatars link to the repo's commits-by-author search; fall
back to profile or `mailto:`.
- Trailer parsing uses `net/mail.ParseAddress`, scans only the trailing
paragraph, filters out the commit's own author/committer.
- Drops the non-standard `Co-committed-by:` emission on squash merge and
web edits.

Devtest: `/devtest/coauthor-avatars`.

Fixes #25521

----
<img width="353" height="277" alt="image"
src="https://github.com/user-attachments/assets/72092ceb-97ca-4b09-9557-0b72d3c5458e"
/>

<img width="533" height="328"
src="https://github.com/user-attachments/assets/11d0c8f8-8b3f-4f2e-9993-879f1c06bcc5"
/>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

routers/web/repo/commit.go

@@ -14,6 +14,7 @@ import (
 	asymkey_model "gitea.dev/models/asymkey"
 	"gitea.dev/models/db"
 	git_model "gitea.dev/models/git"
+	"gitea.dev/models/gituser"
 	issues_model "gitea.dev/models/issues"
 	"gitea.dev/models/renderhelper"
 	repo_model "gitea.dev/models/repo"
@@ -49,7 +50,7 @@ func RefCommits(ctx *context.Context) {
 	switch {
 	case len(ctx.Repo.TreePath) == 0:
 		Commits(ctx)
-	case ctx.Repo.TreePath == "search":
+	case ctx.Repo.TreePath == "search": // FIXME: legacy dirty design, it conflicts with the FileHistory
 		SearchCommits(ctx)
 	default:
 		FileHistory(ctx)
@@ -396,7 +397,8 @@ func Diff(ctx *context.Context) {
 
 	verification := asymkey_service.ParseCommitWithSignature(ctx, commit)
 	ctx.Data["Verification"] = verification
-	ctx.Data["Author"] = user_model.ValidateCommitWithEmail(ctx, commit)
+	ctx.Data["Author"] = user_model.GetUserByGitAuthor(ctx, commit)
+	ctx.Data["CommitOtherParticipants"] = gituser.BuildAvatarStackData(ctx, commit.AllParticipantIdentities(), nil).Participants[1:]
 	ctx.Data["Parents"] = parents
 	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0
 
@@ -411,7 +413,7 @@ func Diff(ctx *context.Context) {
 	err = git.GetNote(ctx, ctx.Repo.GitRepo, commitID, note)
 	if err == nil {
 		ctx.Data["NoteCommit"] = note.Commit
-		ctx.Data["NoteAuthor"] = user_model.ValidateCommitWithEmail(ctx, note.Commit)
+		ctx.Data["NoteAuthor"] = user_model.GetUserByGitAuthor(ctx, note.Commit)
 		rctx := renderhelper.NewRenderContextRepoComment(ctx, ctx.Repo.Repository, renderhelper.RepoCommentOptions{CurrentRefSubURL: "commit/" + util.PathEscapeSegments(commitID)})
 		htmlMessage := template.HTML(template.HTMLEscapeString(string(charset.ToUTF8WithFallback(note.Message, charset.ConvertOpts{}))))
 		ctx.Data["NoteRendered"] = markup.PostProcessCommitMessage(rctx, htmlMessage)
@@ -461,7 +463,7 @@ func RawDiff(ctx *context.Context) {
 }
 
 func processGitCommits(ctx *context.Context, gitCommits []*git.Commit) ([]*git_model.SignCommitWithStatuses, error) {
-	commits, err := git_service.ConvertFromGitCommit(ctx, gitCommits, ctx.Repo.Repository)
+	commits, err := git_service.ConvertFromGitCommit(ctx, gitCommits, ctx.Repo.Repository, ctx.Repo.RefFullName)
 	if err != nil {
 		return nil, err
 	}