fix: use stable per-channel owner worktree to preserve session across tasks

Owner worktree path was per-task (data/workspaces/{folder}/tasks/{taskId}/owner/),
causing Claude SDK to treat each new task as a different project and lose session
context. Now uses a stable per-channel path (data/workspaces/{folder}/owner/).

- Channel isolation preserved (different folders get different worktrees)
- Session persists across tasks (same path = same Claude SDK project)
- Reviewer snapshot still reads from owner worktree correctly
- Fix stale approvedHead reference from cherry-pick conflict

src/paired-execution-context.ts

@@ -227,6 +227,8 @@ export function preparePairedExecutionContext(args: {
         updated_at: now,
       });
     }
+    // Use a stable per-channel worktree (not per-task) so the Claude SDK
+    // session persists across tasks. Different channels still get isolation.
     workspace = provisionOwnerWorkspaceForPairedTask(latestTask.id);
   } else {
     const reviewerWorkspace = prepareReviewerWorkspaceForExecution(latestTask);
@@ -424,7 +426,6 @@ export function completePairedExecutionContext(args: {
           {
             taskId,
             verdict,
-            approvedHead,
             approvedSourceRef,
             summary: args.summary?.slice(0, 100),
           },