sessions: fix worktree-created task dispatch (#317598)

* fix worktree-created task dispatch

Only dispatch worktree-created tasks for newly-created sessions once a concrete worktree is available. Keep restored sessions from re-running setup tasks on window open while still tracking pending untitled sessions created before the dispatcher starts.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* fix worktree task replacement tracking

Avoid wall-clock restored-session checks and only allow committed replacements from still-pending tracked sessions. This prevents restored or already-dispatched sessions from re-running worktreeCreated tasks while preserving pending untitled session dispatch.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>