feat: UFS session lifecycle — lazy init per connection via http_get_ufs()

Redesign UFS session management. Lazy init per HTTPC connection via http_get_ufs() in HTTPX. Solves UFSD reconnect, eliminates per-request ufsnew/ufsfree overhead in mvsMF, prepares for Keep-Alive. ACEE cleared between requests in httprese.c. ESTAE must call http_close on worker abend.

Ref: Notion TASK-41