Apply slug immediately for never-published nodes

staged_slug existed to protect a live public URL from changing until
an editor explicitly publishes - correct once a node has a head, but
nodes_controller#update wrote to it unconditionally, so a brand-new
node being renamed before its first-ever publish showed a stale slug
in previews (e.g. nodes#new's resulting-path preview) that silently
diverged from what would actually go live.

Node#staged_slug= now applies directly to slug when head is blank -
nothing is live yet, so there's nothing to protect. Once head is
present, defers to staged_slug exactly as before. Verified both paths
directly: a never-published node's slug now updates immediately, and
an already-published node's rename still stays deferred until the
next publish, unchanged from existing behavior.

0 files changed, 0 insertions, 0 deletions