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>

modules/repository/commits.go

@@ -9,19 +9,15 @@ import (
 	"net/url"
 	"time"
 
-	"gitea.dev/models/avatars"
 	repo_model "gitea.dev/models/repo"
 	user_model "gitea.dev/models/user"
-	"gitea.dev/modules/cache"
-	"gitea.dev/modules/cachegroup"
 	"gitea.dev/modules/git"
 	"gitea.dev/modules/gitrepo"
-	"gitea.dev/modules/log"
-	"gitea.dev/modules/setting"
 	api "gitea.dev/modules/structs"
 )
 
 // PushCommit represents a commit in a push operation.
+// This struct is marshaled as JSON (see ActionContent2Commits)
 type PushCommit struct {
 	Sha1           string
 	Message        string
@@ -33,6 +29,7 @@ type PushCommit struct {
 }
 
 // PushCommits represents list of commits in a push operation.
+// This struct is marshaled as JSON (see ActionContent2Commits)
 type PushCommits struct {
 	Commits    []*PushCommit
 	HeadCommit *PushCommit
@@ -128,26 +125,6 @@ func (pc *PushCommits) ToAPIPayloadCommits(ctx context.Context, repo *repo_model
 	return commits, headCommit, nil
 }
 
-// AvatarLink tries to match user in database with e-mail
-// in order to show custom avatar, and falls back to general avatar link.
-func (pc *PushCommits) AvatarLink(ctx context.Context, email string) string {
-	size := avatars.DefaultAvatarPixelSize * setting.Avatar.RenderedSizeFactor
-
-	v, _ := cache.GetWithContextCache(ctx, cachegroup.EmailAvatarLink, email, func(ctx context.Context, email string) (string, error) {
-		u, err := user_model.GetUserByEmail(ctx, email)
-		if err != nil {
-			if !user_model.IsErrUserNotExist(err) {
-				log.Error("GetUserByEmail: %v", err)
-				return "", err
-			}
-			return avatars.GenerateEmailAvatarFastLink(ctx, email, size), nil
-		}
-		return u.AvatarLinkWithSize(ctx, size), nil
-	})
-
-	return v
-}
-
 // CommitToPushCommit transforms a git.Commit to PushCommit type.
 func CommitToPushCommit(commit *git.Commit) *PushCommit {
 	return &PushCommit{