Fix CODEOWNERS review request attribution using comment metadata (#36348)

Fixes #36333

## Problem

When CODEOWNERS automatically assigns reviewers to a pull request, the
timeline incorrectly shows the PR author as the one who requested the
review (e.g., "PR_AUTHOR requested review from CODE_OWNER"). This is
misleading since the action was triggered automatically by CODEOWNERS
rules, not by the PR author.

## Solution

Store CODEOWNERS attribution in comment metadata instead of changing the
doer user:
- Add `SpecialDoerName` field to `CommentMetaData` struct (value:
`"CODEOWNERS"` for CODEOWNERS-triggered requests)
- Pass `isCodeOwners=true` to `AddReviewRequest` and
`AddTeamReviewRequest` functions
- Template can check this metadata to show appropriate attribution
message

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/graph/commits.tmpl

@@ -40,14 +40,14 @@
 						{{end}}
 					</span>
 
-					<span class="author flex-text-inline">
+					<span class="flex-text-inline tw-text-12">
 						{{$userName := $commit.Commit.Author.Name}}
 						{{if $commit.User}}
 							{{if and $commit.User.FullName DefaultShowFullName}}
 								{{$userName = $commit.User.FullName}}
 							{{end}}
 							{{ctx.AvatarUtils.Avatar $commit.User 18}}
-							<a href="{{$commit.User.HomeLink}}">{{$userName}}</a>
+							<a class="muted" href="{{$commit.User.HomeLink}}">{{$userName}}</a>
 						{{else}}
 							{{ctx.AvatarUtils.AvatarByEmail $commit.Commit.Author.Email $userName 18}}
 							{{$userName}}