feat: comments marked as decisions, on top of the ticket and searchable

Whoever can change the ticket flags a comment as a decision (new event
CommentDecisionMarkedEvent on the comment). The ticket page lists its
decisions above the description, with a link to the comment in the
conversation (`?comment=<id>` scrolls to it and points at it), and the
search palette finds them by their text across my projects.

API: markDecision / PUT-DELETE /api/comments/{id}/decision; Issue.decisions
and GET /api/issues/{issue}/decisions; decisions(projectId?, search) and
GET /api/projects/{project}/decisions, GET /api/me/decisions. MCP:
mark_decision, search_decisions, and get_issue includes them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/infrastructure/src/lib/adapters/graphql-collaboration.gateways.ts

@@ -23,6 +23,7 @@ import {
   EditCommentDocument,
   IssueCommentsDocument,
   ReactToCommentDocument,
+  MarkDecisionDocument,
   PublishReleaseDocument,
   ReleaseBurnupDocument,
   ReleaseNotesDraftDocument,
@@ -75,6 +76,12 @@ export class GraphqlCommentsGateway extends CommentsGateway {
       .mutate(DeleteCommentDocument, { commentId })
       .pipe(map((d) => toCommandResult(d.deleteComment)));
   }
+
+  markDecision(commentId: string, on: boolean): Observable<CommandResult> {
+    return this.gql
+      .mutate(MarkDecisionDocument, { commentId, on })
+      .pipe(map((d) => toCommandResult(d.markDecision)));
+  }
 }
 
 @Injectable()