sessions: fix Show All Sessions filter out of sync with view on reload (#306435)

* sessions: fix Show All Sessions filter out of sync with view on reload

The IsWorkspaceGroupCappedContext context key was never initialized from
persisted storage on reload, causing the menu checkmark to always show
as checked (default true) regardless of the stored value.

Fix by binding the context key in the constructor and syncing it with
the persisted SessionsList state in renderBody. Also fix the Reset
action which was resetting the internal state but not the context key.

Co-authored-by: Copilot <[email protected]>

* use sessionsControl as source of truth for reset context key

Co-authored-by: Copilot <[email protected]>

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Co-authored-by: Copilot <[email protected]>