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

- Merge steeringComments and comments into unified comments field in Task type
- Update TaskStore to use single comments array instead of separate steeringComments
- Add database migration to convert existing steeringComments to comments
- Update executor to inject all comments into AI execution context
- Update dashboard SteeringTab to use unified comments API
- Update CLI task steer command to use comments field
- Update PR comment handler to add comments via unified API

packages/cli/src/commands/task.ts

@@ -979,7 +979,7 @@ export async function runTaskSteer(id: string, message?: string, projectName?: s
   // Add steering comment
   let task;
   try {
-    task = await store.addSteeringComment(id, trimmed, "user");
+    task = await store.addComment(id, trimmed, "user");
   } catch (err: any) {
     if (err.code === "ENOENT") {
       console.error(`Error: Task not found: ${id}`);