Connect original MR commit review snapshots and captured selections #638

Connect captured original MR commit reads to an immutable review snapshot and selection fingerprint. Single known parent uses original commit refs; unknown/root/multiple parents stay unselectable. Strict literal files/rows only; no MR-wide refs, malformed paths or forged row selections. An account/provider-bound auto-dispose controller discards obsolete reads/errors and changes its session on reload. Test first. Private-save reservation/recovery and UI remain next; this read snapshot does not authorize writes. Related to MW-07, #634 and #636.