* fix(sessions): align archive-cascade count with executed list
When archiving a parent session, the dialog showed the total descendant
count but the actual archive request skipped already-archived
descendants — so the toast/result didn't match what the user was told.
Collect descendants once, then filter per-action: hard-delete cascades
to every descendant; archive skips already-archived ones. Dialog count
and the ID list passed to archiveSessions/deleteSessions now agree.
* fix(sessions): snapshot descendant IDs at dialog open
Address Greptile review: handleDeleteSession populated the dialog
count from a fresh collectDescendants() call, then confirmDeleteSession
re-collected at confirm time — so a background sync that mutated
childrenMap while the dialog was open could re-introduce the same
count-vs-executed mismatch this PR fixed.
Store the computed descendant IDs in deleteSessionConfirm and pass
them through to executeDeleteSession, so the executed list is always
the snapshot the user was shown. The no-dialog direct-execute path
also routes through the snapshot for consistency.
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Co-authored-by: vhqtvn <8930337+vhqtvn@users.noreply.github.com>
