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/api/tracker/application/src/lib/event-handlers/event-handlers.ts

@@ -3,6 +3,7 @@ import { CommentAddedEventHandler } from './comment-added.event-handler';
 import { CommentDeletedEventHandler } from './comment-deleted.event-handler';
 import { CommentEditedEventHandler } from './comment-edited.event-handler';
 import { CommentReactedEventHandler } from './comment-reacted.event-handler';
+import { CommentDecisionMarkedEventHandler } from './comment-decision-marked.event-handler';
 import { IssueVotedEventHandler } from './issue-voted.event-handler';
 import { IssueAssignedEventHandler } from './issue-assigned.event-handler';
 import { IssueCreatedEventHandler } from './issue-created.event-handler';
@@ -50,6 +51,7 @@ export const EVENT_HANDLERS = [
   CommentDeletedEventHandler,
   CommentEditedEventHandler,
   CommentReactedEventHandler,
+  CommentDecisionMarkedEventHandler,
   IssueVotedEventHandler,
   IssueAssignedEventHandler,
   IssueCreatedEventHandler,