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/DISCUSSION_TEMPLATE/q-a.yaml

@@ -0,0 +1,17 @@
+title: 'Q&A'
+labels: []
+body:
+  - type: markdown
+    attributes:
+      value: |
+        Use this space for questions, ideas, and general discussion about todo.nvim.
+        For bug reports, please [open an issue](https://github.com/barrettruth/todo.nvim/issues/new/choose) instead.
+  - type: textarea
+    attributes:
+      label: Question or topic
+    validations:
+      required: true
+  - type: textarea
+    attributes:
+      label: Context
+      description: Any relevant details (Neovim version, config, screenshots)