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/domain/src/lib/events/comment-decision-marked.event.ts

@@ -0,0 +1,17 @@
+import { AutowiredEvent } from '@task-stream/api/shared/domain';
+import { TrackerEvent } from './tracker.event';
+
+/** A comment was marked as a decision of the ticket, or unmarked. */
+@AutowiredEvent
+export class CommentDecisionMarkedEvent extends TrackerEvent {
+  constructor(
+    actorId: string,
+    commentId: string,
+    projectId: string,
+    readonly issueId: string,
+    /** False: it is no longer a decision. */
+    readonly decision: boolean,
+  ) {
+    super(actorId, commentId, projectId);
+  }
+}

libs/api/tracker/domain/src/lib/events/index.ts

@@ -15,6 +15,7 @@ export * from './issue-release-changed.event';
 export * from './comment-added.event';
 export * from './comment-edited.event';
 export * from './comment-reacted.event';
+export * from './comment-decision-marked.event';
 export * from './comment-deleted.event';
 export * from './release-created.event';
 export * from './release-updated.event';