Ports the intent of the lost CB-576 commit c393600 (worker/cb576-01a04b-17,
never merged, package dev.ltms.bridged.*) onto main's dev.ltms.fleet.*
tree. Adds FakeWorktrees.markGone (tracks which add()'d worktree paths
still "exist", mirroring GitWorktrees.hasUncommitted's Files.exists guard
for the already-gone case) and a regression test,
releaseStillStopsPaneAndNotifiesWhenWorktreeIsGone, asserting that
SessionManager.release still fires notifyReleased, stops the pane, and
falls through to remove() when the worktree is already gone.
Dai Ha
8308c0b68f