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>

web_src/css/features/gitgraph.css

@@ -46,10 +46,6 @@
   height: 20px;
 }
 
-#git-graph-container li .author {
-  color: var(--color-text-light);
-}
-
 #git-graph-container li .time {
   color: var(--color-text-light-3);
   font-size: 80%;