build: add .editorconfig for consistent code formatting

Adds a root .editorconfig with basic formatting conventions
(UTF-8, LF line endings, trailing whitespace trimming, final
newline, and indentation rules for Kotlin, Java, Gradle, XML,
YAML/JSON, and Markdown) so contributors get consistent
defaults across editors and IDEs.

Fixes #964

Author: kikoso

.editorconfig

@@ -0,0 +1,35 @@
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4
+
+[*.{kt,kts}]
+indent_size = 4
+max_line_length = 100
+ij_kotlin_allow_trailing_comma = true
+ij_kotlin_allow_trailing_comma_on_call_site = true
+ij_kotlin_packages_to_use_import_on_demand = unset
+
+[*.java]
+indent_size = 4
+max_line_length = 100
+
+[*.{xml,gradle}]
+indent_size = 4
+
+[*.{yml,yaml,json}]
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false
+
+[*.{bat,cmd}]
+end_of_line = crlf
+
+[Makefile]
+indent_style = tab