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.

.gitattributes

@@ -1,2 +1,8 @@
 # Generated files
-HellionChat/Resources/Language.*.resx linguist-generated=true
+HellionChat/Resources/Language.*.resx linguist-generated=true
+* text=auto eol=lf
+*.cs text eol=lf
+*.yml text eol=lf
+*.yaml text eol=lf
+*.md text eol=lf
+*.json text eol=lf