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/presenters/src/lib/http/comments.controller.ts

@@ -6,6 +6,7 @@ import {
   Param,
   Patch,
   Post,
+  Put,
 } from '@nestjs/common';
 import { ApiOkResponse, ApiOperation, ApiTags } from '@nestjs/swagger';
 import { User } from '@task-stream/api/identity/domain';
@@ -54,6 +55,29 @@ export class CommentsController {
     return this.comments.react(me.id, commentId, body.emoji, body.on);
   }
 
+  @Put(':commentId/decision')
+  @ApiOperation({
+    summary: 'Mark a comment as a decision of its ticket',
+    description:
+      'Whoever can change the ticket. Decisions are shown above the ticket and searchable (GET …/decisions).',
+  })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  markDecision(@CurrentUser() me: User, @Param('commentId') commentId: string) {
+    return this.comments.markDecision(me.id, commentId, true);
+  }
+
+  @Delete(':commentId/decision')
+  @ApiOperation({ summary: 'It is no longer a decision' })
+  @ApiOkResponse({ type: CommandResultDto })
+  @ApiCommandErrors()
+  unmarkDecision(
+    @CurrentUser() me: User,
+    @Param('commentId') commentId: string,
+  ) {
+    return this.comments.markDecision(me.id, commentId, false);
+  }
+
   @Delete(':commentId')
   @ApiOperation({ summary: 'Delete a comment (author or project admin)' })
   @ApiOkResponse({ type: CommandResultDto })