ci: add GitHub workflows and issue templates

Problem: need CI for tests, quality checks, luarocks publishing,
and structured issue/discussion templates.

Solution: add test, quality, and luarocks workflows mirroring
diffs.nvim conventions. Add bug report, feature request, and
Q&A templates.

.github/ISSUE_TEMPLATE/config.yaml

@@ -0,0 +1,5 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Questions
+    url: https://github.com/barrettruth/todo.nvim/discussions
+    about: Ask questions and discuss ideas