Update code guidelines from platform

resources/guidelines/code/core/AGENTS.md

@@ -0,0 +1,67 @@
+Directory contains 11 Shopware 6 core development guidelines covering architecture, testing, and code quality.
+
+**Usage**: Match your task in the matrix → Load relevant guideline files for detailed rules and patterns.
+
+---
+
+## Quick Reference Matrix
+
+| Scenario | Required Guidelines |
+|----------|-------------------|
+| **Creating new service** | decorator-pattern, internal, final-and-internal |
+| **Writing tests** | unit-tests, writing-code-for-static-analysis |
+| **Database changes** | database-migations, feature-flags |
+| **Adding public API** | extendability, decorator-pattern, internal |
+| **Breaking changes** | feature-flags, database-migations |
+| **Error handling** | domain-exceptions, writing-code-for-static-analysis |
+| **PHP 8 features** | 6.5-new-php-language-features, writing-code-for-static-analysis |
+| **Architecture decisions** | adr, extendability |
+| **Service decoration** | decorator-pattern, extendability |
+| **Type safety** | writing-code-for-static-analysis, 6.5-new-php-language-features |
+
+---
+
+::: info
+This document represents core guidelines and has been mirrored from the core in our Shopware 6 repository.
+You can find the original version [here](https://github.com/shopware/shopware/blob/trunk/coding-guidelines/core/AGENTS.md)
+:::
+
+## Guideline Registry
+
+### Core Architecture
+**extendability.md**
+- **Scope**: Patterns for extension (Decoration/Factory/Visitor/Mediator/Adapter)
+
+**decorator-pattern.md**
+- **Scope**: Service decoration rules, abstract classes, getDecorated()
+
+**adr.md**
+- **Scope**: Architecture decision record template
+
+### API Design
+**internal.md**
+- **Scope**: @internal annotation usage, private API marking
+
+**final-and-internal.md**
+- **Scope**: @final annotation, BC rules for classes
+
+### Development Practices
+**feature-flags.md**
+- **Scope**: Feature toggles, gradual rollout, BC management
+
+**database-migations.md**
+- **Scope**: Migration rules, destructive changes, blue-green deployment
+
+### Code Quality
+**unit-tests.md**
+- **Scope**: Test coverage, mocking strategy, test design principles
+
+**writing-code-for-static-analysis.md**
+- **Scope**: PHPStan compliance, type safety, static analysis patterns
+
+**domain-exceptions.md**
+- **Scope**: Exception factory pattern, error codes, HTTP status mapping
+
+### Language Features
+**6.5-new-php-language-features.md**
+- **Scope**: PHP 8.1+ features (enums/readonly/promoted props/match)