Refactor testing documentation into organized folder structure

.github/copilot-instructions.md

@@ -103,7 +103,7 @@ These principles should guide all development decisions, code reviews, and featu
 - **Dependencies**: `cargo machete` (mandatory before commits - no unused dependencies)
 - **Build**: `cargo build`
 - **Test**: `cargo test`
-- **Unit Tests**: When writing unit tests, follow conventions described in [`docs/contributing/testing.md`](../docs/contributing/testing.md)
+- **Unit Tests**: When writing unit tests, follow conventions described in [`docs/contributing/testing/`](../docs/contributing/testing/)
 - **E2E Tests**: `cargo run --bin e2e-tests-full` (comprehensive - all tests) or individual tests:
   - `cargo run --bin e2e-provision-tests` - Infrastructure provisioning tests
   - `cargo run --bin e2e-config-tests` - Configuration validation tests

README.md

@@ -330,7 +330,7 @@ This project follows a structured development roadmap to evolve from the current
 │   │   ├── commit-process.md # Commit process and pre-commit checks
 │   │   ├── error-handling.md # Error handling principles
 │   │   ├── module-organization.md # Module organization conventions
-│   │   └── testing.md       # Testing conventions
+│   │   └── testing/         # Testing conventions and guides
 │   ├── features/            # Feature specifications and documentation
 │   ├── research/            # Research and analysis documents
 │   └── *.md                 # Various documentation files

docs/contributing/error-handling.md

@@ -758,7 +758,7 @@ When reviewing error handling code, verify:
 
 - [Development Principles](../development-principles.md) - Core principles including observability and actionability
 - [Contributing Guidelines](./README.md) - General contribution guidelines
-- [Testing Conventions](./testing.md) - Testing error scenarios
+- [Testing Conventions](./testing/) - Testing error scenarios
 
 ## 📚 Examples in Codebase
 

docs/contributing/module-organization.md

@@ -601,7 +601,7 @@ create/
 
 ## 🔗 Related Documentation
 
-- [Testing Conventions](./testing.md) - How to organize test code
+- [Testing Conventions](./testing/) - How to organize test code
 - [Error Handling Guide](./error-handling.md) - Error type design principles
 - [Development Principles](../development-principles.md) - Overall code quality standards