Add AV0105: Use design patterns to communicate intent

_rules/0105.md

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+---
+rule_id: 0105
+rule_category: general
+title: Use design patterns to communicate intent
+severity: 2
+---
+[Design patterns](https://en.wikipedia.org/wiki/Software_design_pattern) are proven, named solutions to recurring design problems. Using them lets you communicate the structure and intent of your code in a single recognizable term: *Repository*, *Factory*, *Strategy*, *Observer*, *Decorator*, and so on.
+
+When you refactor a complex piece of code into a well-known pattern:
+- Other developers immediately understand the structure without having to reverse-engineer it.
+- The code gains a shared vocabulary that transcends the codebase.
+- It becomes easier to reason about responsibilities and extension points.
+
+> [!TIP]
+> If you cannot assign a single design pattern to a class, it may be doing more than one thing. Consider splitting it up.
+
+> [!TIP]
+> Don't force a pattern onto code that doesn't need it — a pattern is a tool, not a goal. Prefer simplicity when the problem doesn't warrant the extra structure.