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/comments.service.ts

@@ -1,14 +1,22 @@
 import { CommandRunner } from '@task-stream/api/shared/application';
 import { Injectable } from '@nestjs/common';
 import { QueryBus } from '@nestjs/cqrs';
-import { CommentReadModel } from '@task-stream/api/tracker/domain';
+import {
+  CommentReadModel,
+  DecisionReadModel,
+} from '@task-stream/api/tracker/domain';
 import { AddCommentCommand } from './commands/add-comment.command';
 import { CommandResult } from './commands/command-result';
 import { DeleteCommentCommand } from './commands/delete-comment.command';
 import { EditCommentCommand } from './commands/edit-comment.command';
 import { ReactToCommentCommand } from './commands/react-to-comment.command';
+import { MarkDecisionCommand } from './commands/mark-decision.command';
 import { Page } from './ports/find-issues.repository';
 import { GetCommentsQuery } from './queries/get-comments.query';
+import {
+  GetIssueDecisionsQuery,
+  SearchDecisionsQuery,
+} from './queries/decisions.query';
 
 @Injectable()
 export class CommentsService {
@@ -50,6 +58,35 @@ export class CommentsService {
     );
   }
 
+  /** Marks it as a decision of its ticket (`on`) or unmarks it: the team does. */
+  markDecision(
+    actorId: string,
+    commentId: string,
+    on: boolean,
+  ): Promise<CommandResult> {
+    return this.commands.execute(
+      new MarkDecisionCommand(actorId, commentId, on),
+    );
+  }
+
+  /** A ticket's decisions, oldest first. */
+  decisions(
+    viewerId: string | null,
+    issueId: string,
+  ): Promise<CommentReadModel[]> {
+    return this.queryBus.execute(new GetIssueDecisionsQuery(viewerId, issueId));
+  }
+
+  /** Decisions by their text: of a project, or of all mine without one. */
+  searchDecisions(
+    viewerId: string | null,
+    filter: { projectId?: string; search?: string; limit?: number },
+  ): Promise<DecisionReadModel[]> {
+    return this.queryBus.execute(
+      new SearchDecisionsQuery(viewerId, { limit: 20, ...filter }),
+    );
+  }
+
   delete(actorId: string, commentId: string): Promise<CommandResult> {
     return this.commands.execute(new DeleteCommentCommand(actorId, commentId));
   }