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.

.markdownlint.json

@@ -0,0 +1,7 @@
+{
+    "MD007": { "indent": 4 },
+    "MD013": false,
+    "MD029": false,
+    "MD033": false,
+    "MD041": false
+}