feat: side-thread task kind (Muse role alignment phase 2)

Tasks gain kind='main'|'side' (NULL=main). A side thread hangs under a
parent task, defaults to the local executor, never builds a worktree,
branch or container unless explicitly asked, and writes its conclusion
back to the parent via task_followups on terminal transition.

- server: kind validation + side-thread gates (parent required, no
  coordinator_parts/upload_id/environment_id, parent must not be a
  coordinator), local executor default, GET /tasks kind filter,
  /worktree 404 and /fork /merge /pr 409 for side threads.
- worker: side-default shunt in _run_attempt (no-worktree scratch cwd,
  in-memory plan=1 when a repo is present, seed/checkpoint skipped),
  _writeback_side_thread, marker task-create kind field + inheritance,
  side threads excluded from marker spawn counts.
- host/sandbox: --no-worktree plumbing for dispatch/goal/popen
  (Local + Docker), scratch cwd work/side-threads/<task-id>.
- console (classic only): kind filter + [旁聊] rows + '开旁聊' entry,
  side-thread dispatch mode, side-thread list in detail, merge/PR/fork
  hidden for side threads; build exit 0, console.html sha df39db5a.
- tests: new test_sidethread.py (29 tests) + kind backfill tests in
  test_p2_migrations.py; full cloud suite 3900 tests OK (skipped=13).

Design: verification/codex-muse-role-alignment-design-20261108.md
Summary: verification/codex-muse-role-align-p1p2-20261108.md
Local only: not pushed, not merged, not deployed.

cloud/console-react/src/api/paths.ts

@@ -29,14 +29,19 @@ export const paths = {
   environmentsCreate: "/environments",
   environmentArchive: (id: string) => "/environments/" + enc(id) + "/archive",
   tasks: (pid: string) => "/tasks?project_id=" + enc(pid),
-  tasksPage: (pid: string, limit: number, offset: number, status?: string, executor?: string, q?: string) => {
+  tasksPage: (pid: string, limit: number, offset: number, status?: string, executor?: string, q?: string, kind?: string) => {
     let u = "/tasks?project_id=" + enc(pid) + "&limit=" + limit + "&offset=" + offset + "&order=desc";
     if (status) u += "&status=" + enc(status);
     if (executor) u += "&executor=" + enc(executor);
     if (q && q.trim()) u += "&q=" + enc(q.trim());
+    if (kind) u += "&kind=" + enc(kind);
+    return u;
+  },
+  tasksByParent: (pid: string, parent: string, kind?: string) => {
+    let u = "/tasks?project_id=" + enc(pid) + "&parent_task_id=" + enc(parent);
+    if (kind) u += "&kind=" + enc(kind);
     return u;
   },
-  tasksByParent: (pid: string, parent: string) => "/tasks?project_id=" + enc(pid) + "&parent_task_id=" + enc(parent),
   tasksCreate: "/tasks",
   task: (id: string) => "/tasks/" + enc(id),
   taskAction: (id: string, kind: string) => "/tasks/" + enc(id) + "/" + kind,