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/base.css

@@ -469,19 +469,6 @@ a.label,
   box-shadow: 1px 1px 0 0 var(--color-secondary);
 }
 
-.ui.comments .comment .text {
-  margin: 0;
-}
-
-.ui.comments .comment .text,
-.ui.comments .comment .author {
-  color: var(--color-text);
-}
-
-.ui.comments .comment a.author:hover {
-  color: var(--color-primary);
-}
-
 .ui.comments .comment .metadata {
   color: var(--color-text-light-2);
 }
@@ -562,6 +549,7 @@ img.ui.avatar,
   color: var(--color-purple) !important;
 }
 
+/* it is different from tw-text-black: this one changes in dark theme */
 .text.black {
   color: var(--color-text) !important;
 }