Add AV0115 guideline (#304)

Split from #298.

Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

_rules/0115.md

@@ -0,0 +1,14 @@
+---
+rule_id: 0115
+rule_category: general
+title: Keep It Simple Stupid (KISS)
+severity: 1
+---
+The simplest solution that fully solves the problem is almost always the best one. Complexity accumulates quickly and makes code harder to read, test, debug and change.
+
+Avoid:
+- Over-engineering for problems that don't yet exist.
+- Layers of abstraction that add no value in the current context.
+- Clever tricks that are hard to understand without deep knowledge of the language.
+
+A method that a junior developer can read and understand in one pass is almost always preferable to an elegant but opaque alternative. Simplicity is a feature, not a shortcut.