fix(lint): make mbake format the Makefile the same on every machine

The repository installs mbake unpinned and shipped no .bake.toml, so the
Makefile's final newline depended on the mbake version:

- mbake 1.4.6 (e.g. the pkgmgr venv that wins on a host PATH) defaults
  to ensure_final_newline = false: `mbake format` strips the newline and
  `mbake format --check` accepts the stripped file.
- mbake 1.5.0 (what pip installs today) rejects the same file with
  "Missing final newline", which is what CI reported on PR #1255.

So a local `make autoformat` could strip the newline, the local
lint-makefile stayed green, and CI failed; 6f653ce633 and #1262 had to
restore the newline by hand.

The tracked .bake.toml sets only ensure_final_newline = true, so every
other formatter rule keeps its default. autoformat.sh and makefile.sh
pass it with --config, so the result no longer depends on the version
or on the directory mbake runs from. Checked with both versions: main's
Makefile passes `--check --config .bake.toml`, and a copy without the
final newline fails it with "Missing final newline".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.bake.toml

@@ -0,0 +1,2 @@
+[formatter]
+ensure_final_newline = true

scripts/lint/autoformat.sh

@@ -139,8 +139,8 @@ run_mbake() {
 		return 0
 	fi
 	local rc=0
-	mbake format Makefile >/dev/null 2>&1 || rc=$?
-	[[ $rc -eq 0 ]] && { mbake format Makefile >/dev/null 2>&1 || rc=$?; }
+	mbake format --config .bake.toml Makefile >/dev/null 2>&1 || rc=$?
+	[[ $rc -eq 0 ]] && { mbake format --config .bake.toml Makefile >/dev/null 2>&1 || rc=$?; }
 	if [[ $rc -eq 0 ]]; then
 		write_status mbake OK
 	else

scripts/lint/makefile.sh

@@ -17,4 +17,4 @@ if ! command -v mbake >/dev/null 2>&1; then
 	exit 127
 fi
 
-mbake format --check Makefile
+mbake format --check --config .bake.toml Makefile