chore: add Cask + ert-runner test infrastructure

Replace the bare emacs --batch test runner with cask exec ert-runner.
The Makefile test targets now delegate. validate-parens, compile, and
lint stay on bare emacs --batch. Running cask once per file would slow
them down for no real win.

Adds:
- Cask file declaring sources and ert-runner as a dev dep
- .ert-runner config adding . and tests to load-path
- tests/test-helper.el placeholder for future test setup
- .gitignore entry for .cask/

All 88 tests pass in 0.19s via the new path.

1 files changed, 8 insertions, 0 deletions

diff --git a/Cask b/Cask
new file mode 100644
index 0000000..7dea946
--- /dev/null
+++ b/Cask
@@ -0,0 +1,8 @@
+(source gnu)
+(source nongnu)
+(source melpa)
+
+(package-file "gloss.el")
+
+(development
+ (depends-on "ert-runner"))