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/git/commit.go

@@ -11,18 +11,10 @@ import (
 	"os/exec"
 	"strings"
 
-	"gitea.dev/modules/charset"
 	"gitea.dev/modules/git/gitcmd"
 	"gitea.dev/modules/util"
 )
 
-type CommitMessage struct {
-	MessageRaw   string
-	messageUTF8  *string
-	messageTitle *string
-	messageBody  *string
-}
-
 // Commit represents a git commit.
 type Commit struct {
 	Tree // FIXME: bad design, this field can be nil if the commit is from "last commit cache"
@@ -44,30 +36,6 @@ type CommitSignature struct {
 	Payload   string
 }
 
-func (c *CommitMessage) MessageUTF8() string {
-	if c.messageUTF8 == nil {
-		bs := charset.ToUTF8(util.UnsafeStringToBytes(c.MessageRaw), charset.ConvertOpts{ErrorReplacement: []byte{'?'}})
-		c.messageUTF8 = new(util.UnsafeBytesToString(bs))
-	}
-	return *c.messageUTF8
-}
-
-func (c *CommitMessage) MessageTitle() string {
-	if c.messageTitle == nil {
-		s, _, _ := strings.Cut(strings.TrimSpace(c.MessageUTF8()), "\n")
-		c.messageTitle = new(strings.TrimSpace(s))
-	}
-	return *c.messageTitle
-}
-
-func (c *CommitMessage) MessageBody() string {
-	if c.messageBody == nil {
-		_, s, _ := strings.Cut(strings.TrimSpace(c.MessageUTF8()), "\n")
-		c.messageBody = new(strings.TrimSpace(s))
-	}
-	return *c.messageBody
-}
-
 // ParentID returns oid of n-th parent (0-based index).
 // It returns nil if no such parent exists.
 func (c *Commit) ParentID(n int) (ObjectID, error) {