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>

web_src/js/index.ts

@@ -21,7 +21,7 @@ import {initMarkupContent} from './markup/content.ts';
 import {initRepoFileView} from './features/file-view.ts';
 import {initUserExternalLogins, initUserCheckAppUrl} from './features/user-auth.ts';
 import {initRepoPullRequestReview, initRepoIssueFilterItemLabel} from './features/repo-issue.ts';
-import {initRepoEllipsisButton, initCommitStatuses, initCommitFileHistoryFollowRename} from './features/repo-commit.ts';
+import {initRepoEllipsisButton, initCommitStatuses, initAvatarStackPopup, initCommitFileHistoryFollowRename} from './features/repo-commit.ts';
 import {initRepoTopicBar} from './features/repo-home.ts';
 import {initAdminCommon} from './features/admin/common.ts';
 import {initRepoCodeView} from './features/repo-code.ts';
@@ -146,6 +146,7 @@ const initPerformanceTracer = callInitFunctions([
   initRepoRecentCommits,
 
   initCommitStatuses,
+  initAvatarStackPopup,
   initCaptcha,
 
   initUserCheckAppUrl,