chore: add linter & formatter config

Add .editorconfig (LF, Allman), .prettierrc.json, .markdownlint.json,
.yamllint.yaml, .gitattributes and .prettierignore. Extend CI with
format and lint checks.

.editorconfig

@@ -7,12 +7,21 @@ insert_final_newline=false
 
 # JetBrains Rider custom properties for code formatting styles
 resharper_csharp_brace_style=next_line
+# Allman für standard Tooling (VS Code)
+csharp_new_line_before_open_brace = all
+csharp_new_line_before_else = true
+csharp_new_line_before_catch = true
+csharp_new_line_before_finally = true
+
+# Switch-Einrückung
+csharp_indent_case_contents = true
+csharp_indent_switch_labels = true
 
 resharper_csharp_braces_for_foreach=not_required
 resharper_csharp_braces_for_for=not_required
 resharper_csharp_braces_for_while=not_required
 charset=utf-8
-end_of_line=crlf
+end_of_line=lf
 
 # Microsoft .NET properties
 csharp_new_line_before_members_in_object_initializers=false
@@ -142,7 +151,7 @@ resharper_web_config_module_not_resolved_highlighting=warning
 resharper_web_config_type_not_resolved_highlighting=warning
 resharper_web_config_wrong_module_highlighting=warning
 
-[{*.har,*.jsb2,*.jsb3,*.json,*.jsonc,*.postman_collection,*.postman_collection.json,*.postman_environment,*.postman_environment.json,.babelrc,.eslintrc,.prettierrc,.stylelintrc,bowerrc,jest.config}]
+[{*.har,*.jsb2,*.jsb3,*.json,*.jsonc,*.postman_collection,*.postman_collection.json,*.postman_environment,*.postman_environment.json,.babelrc,.eslintrc,.prettierrc,.prettierrc.json,.markdownlint.json,.yamllint.json,.stylelintrc,bowerrc,jest.config}]
 indent_style=space
 indent_size=2
 
@@ -154,3 +163,5 @@ indent_size=2
 indent_style=space
 indent_size=4
 tab_width=4
+[*.md]
+trim_trailing_whitespace=false