fix(workflow): wt-new branches with --no-track (no inherited origin/main upstream)

Branching off origin/main set the new branch's upstream to origin/main, so a
bare `git push` failed with a name-mismatch and suggested the dangerous
`git push origin HEAD:main`. Add --no-track so the branch carries no upstream
until the first `git push -u origin <branch>` sets the right one — keeping the
fresh-from-origin/main base without the tracking side-effect.

Add a test-wt.sh assertion that a new branch has no upstream, and note the
behaviour + first-push form in ADR-0059 / CLAUDE.md.

scripts/test-wt.sh

@@ -37,6 +37,10 @@ out="$(run bash "$WT_NEW" feat/thing-one 2>/dev/null)"
 check "prints target path" "$target1" "$out"
 check "worktree dir exists" "yes" "$(exists "$target1")"
 check "worktree on the new branch" "feat/thing-one" "$(git -C "$target1" rev-parse --abbrev-ref HEAD)"
+# It must NOT inherit origin/main as upstream (else a bare `git push` errors
+# with a name-mismatch and suggests the dangerous `HEAD:main`). No upstream
+# until the first `git push -u` sets the right one.
+check "new branch has no upstream" "none" "$(git -C "$target1" rev-parse --abbrev-ref '@{upstream}' 2>/dev/null || echo none)"
 
 echo "--- wt-new refuses to clobber an existing branch ---"
 set +e; run bash "$WT_NEW" feat/thing-one >/dev/null 2>&1; rc=$?; set -e