feat(reactions): add emoji reactions for comments and issue descriptions

Add Slack-style emoji reactions to comments and issue descriptions with
full-stack support: database tables, REST API endpoints, real-time
WebSocket sync, optimistic UI updates, and inbox notifications.

- New `comment_reaction` and `issue_reaction` tables with migrations
- POST/DELETE endpoints for adding/removing reactions on both comments
  and issue descriptions
- Real-time WS events (reaction:added/removed, issue_reaction:added/removed)
- Shared ReactionBar component with quick emoji picker and full emoji-mart
  picker (lazy-loaded)
- Optimistic add/remove with rollback on failure
- Inbox notifications for comment author and issue creator when reacted to
- Reactions included in timeline, comment list, and issue detail responses

apps/web/shared/api/client.ts

@@ -17,6 +17,8 @@ import type {
   InboxItem,
   IssueSubscriber,
   Comment,
+  Reaction,
+  IssueReaction,
   Workspace,
   WorkspaceRepo,
   MemberWithUser,
@@ -225,6 +227,34 @@ export class ApiClient {
     await this.fetch(`/api/comments/${commentId}`, { method: "DELETE" });
   }
 
+  async addReaction(commentId: string, emoji: string): Promise<Reaction> {
+    return this.fetch(`/api/comments/${commentId}/reactions`, {
+      method: "POST",
+      body: JSON.stringify({ emoji }),
+    });
+  }
+
+  async removeReaction(commentId: string, emoji: string): Promise<void> {
+    await this.fetch(`/api/comments/${commentId}/reactions`, {
+      method: "DELETE",
+      body: JSON.stringify({ emoji }),
+    });
+  }
+
+  async addIssueReaction(issueId: string, emoji: string): Promise<IssueReaction> {
+    return this.fetch(`/api/issues/${issueId}/reactions`, {
+      method: "POST",
+      body: JSON.stringify({ emoji }),
+    });
+  }
+
+  async removeIssueReaction(issueId: string, emoji: string): Promise<void> {
+    await this.fetch(`/api/issues/${issueId}/reactions`, {
+      method: "DELETE",
+      body: JSON.stringify({ emoji }),
+    });
+  }
+
   // Subscribers
   async listIssueSubscribers(issueId: string): Promise<IssueSubscriber[]> {
     return this.fetch(`/api/issues/${issueId}/subscribers`);