chore: add .editorconfig for consistent code formatting

Enforce consistent 4-space indentation for C source files
and proper line ending handling.

.editorconfig

@@ -0,0 +1,21 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+charset = utf-8
+
+[*.{c,h,cpp,hpp}]
+indent_style = space
+indent_size = 4
+
+[*.{yml,yaml}]
+indent_style = space
+indent_size = 2
+
+[*.md]
+trim_trailing_whitespace = false
+
+[Makefile]
+indent_style = tab