Add “Copy Source” to markup comment menu (#36726)

Any user with **read access** to a comment can now copy its raw markdown
source via the `···` context menu — no edit permission required.

Closes #36722.

---------

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

templates/repo/diff/comments.tmpl

@@ -64,7 +64,7 @@
 				<span class="no-content">{{ctx.Locale.Tr "repo.issues.no_content"}}</span>
 			{{end}}
 			</div>
-			<div id="issuecomment-{{.ID}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
+			<div id="{{.HashTag}}-raw" class="raw-content tw-hidden">{{.Content}}</div>
 			<div class="edit-content-zone tw-hidden" data-update-url="{{$.root.RepoLink}}/comments/{{.ID}}" data-content-version="{{.ContentVersion}}" data-context="{{$.root.RepoLink}}" data-attachment-url="{{$.root.RepoLink}}/comments/{{.ID}}/attachments"></div>
 			{{if .Attachments}}
 				{{template "repo/issue/view_content/attachments" dict "Attachments" .Attachments "RenderedContent" .RenderedContent}}