docs(migration): brace ${key} in run-operator-window — bash 5.3 absorbed the ellipsis byte into the var name under set -u

The pilot died at line 93 with 'key<byte>: unbound variable': $key glued to
the U+2026 ellipsis let bash 5.3.9 read the multibyte byte as part of the name.
Braced to ${key}…; proven on /usr/local/bin/bash (repro + fixed form + bash -n).
Nothing was mutated on Forgejo — it failed before the [b] repo-create POST.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/marketplace-polyrepo-migration/migration/run-operator-window.sh

@@ -90,7 +90,7 @@ rollout_one() {
   fi
 
   # (b) create the Forgejo repo (201 created | 409 already exists)
-  say "  [b] create repo open/$key…"
+  say "  [b] create repo open/${key}…"
   body="$(mktemp)"
   code="$(curl -sS -o "$body" -w '%{http_code}' -X POST "$API/orgs/open/repos" \
     -H "Authorization: token $FORGEJO_TOKEN" -H "Content-Type: application/json" \