feat(KB-622): unify steeringComments and comments into single field

- Add database migration to merge steeringComments into comments field
- Update SQLite schema and queries to use unified comments column
- Refactor TaskStore to handle single comments field instead of dual fields
- Update dashboard components (SteeringTab, TaskCard) for unified comments
- Update engine executor and PR comment handler for new field structure
- Remove deprecated steeringComments from types and interfaces

packages/engine/src/pr-comment-handler.ts

@@ -85,10 +85,10 @@ export class PrCommentHandler {
     const text = this.buildSteeringText(prInfo, comment, hasCodeSuggestions);
 
     try {
-      await this.store.addSteeringComment(taskId, text, "agent");
-      prMonitorLog.log(`Added steering comment for PR review #${comment.id}`);
+      await this.store.addComment(taskId, text, "agent");
+      prMonitorLog.log(`Added comment for PR review #${comment.id}`);
     } catch (err) {
-      prMonitorLog.error(`Failed to add steering comment for ${taskId}:`, err);
+      prMonitorLog.error(`Failed to add comment for ${taskId}:`, err);
     }
   }