v0.102.1 — From a worktree, flow finds the work it is in

In short

• next, daily and resume see your works from inside a worktree. Before, they said "nothing in flight" there, because the work folders only exist in the main checkout.
• From the main checkout they say which worktree each work lives in, so "where were we" is answered with a cd.
• Every phase finds its work the same way — by branch, by any MR branch of a train, or by the worktree it was created in — the way the session-start header already did.

Closes #223.