* feat(ui): rename, delete, and toggle sidebar session groups
Sidebar group headers gain a kebab + right-click menu with Rename group,
New group, and Delete group. Rename/delete enumerate every member session
(active + archived, across agents) via unbounded sessions.list queries and
patch category per session; delete keeps sessions and moves them to
Ungrouped. Stored-but-empty groups render as sections, and the sidebar
sort popover gains a persisted Group by toggle (Custom groups / None).
* test(ui): capture sidebar group management UI proof shots
* fix(ui): page session-group enumeration past the gateway's 100-row default
sessions.list caps an absent limit at SESSIONS_LIST_DEFAULT_LIMIT (100), so
the rename/delete member enumeration now walks nextOffset pages explicitly;
a silent cap would strand members in the old group on stores >100 sessions.
* chore(i18n): restore fallback-key tracking for new sidebar group strings after rebase
* chore(i18n): translate new sidebar group strings across locales
5157446a2c
