feat(cli, conversation): Add --from/--until to archive, unify TimeThreshold

[JeanMertz]

Extend jp c archive with --from, --until, and --yes flags to
match the ergonomics already offered by jp c rm. All three filter
flags (--from, --until, --inactive-since) AND-compose when
combined, letting users target a precise slice of conversations by
creation date and inactivity in a single command.

The default no-target behaviour of jp c archive has also been
corrected: instead of opening the picker, it now mirrors jp c show and
resolves to the session's active conversation (falling back through
conversation.default_id to the picker only when no session context is
available).

On the jp c rm side, --from/--until previously accepted raw
ConversationId values. They now accept the full TimeThreshold syntax
(relative durations, absolute dates, and conversation IDs), making both
commands consistent.

TimeThreshold itself gained a new parsing branch: passing a
conversation ID resolves to that conversation's embedded creation
timestamp. This means --from jp-c-… is a convenient shorthand for
"start from the moment that conversation was created", without having to
know or copy the exact date.

Unit tests were added for archive and rm covering the filter
matching logic, load-request routing, and the new TimeThreshold
conversation-ID parsing path.

Signed-off-by: Jean Mertz git@jeanmertz.com