chore: housekeeping — linter & formatter setup

Add .prettierrc.json, .markdownlint.json, .yamllint.yaml, .gitattributes
Run CSharpier, Prettier and markdownlint across the entire codebase.
No logic changes — formatting, using order and line endings only.

.prettierignore

@@ -0,0 +1,4 @@
+bin/
+obj/
+node_modules/
+*.Designer.cs