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.

.yamllint.yaml

@@ -0,0 +1,8 @@
+extends: default
+rules:
+    line-length: disable
+    document-start: disable
+    truthy:
+        allowed-values: ["true", "false", "on"]
+    empty-lines:
+        max: 1