refactor: move legacy migration examples to docs/archive subdirectory

Legacy Content Organization:
✅ MIGRATION EXAMPLES ARCHIVED: Moved legacy migration examples to documentation archive
- docs/archive/migration_examples/: Moved from root directory for better organization
- Contains GPU acceleration migration examples from CUDA to abstraction layer
- Educational/reference material for historical context and migration procedures

✅ LEGACY CONTENT IDENTIFIED:
- GPU Acceleration Migration: From CUDA-specific to backend-agnostic abstraction layer
- Migration Patterns: BEFORE/AFTER code examples showing evolution
- Legacy Import Paths: high_performance_cuda_accelerator, fastapi_cuda_zk_api
- Deprecated Classes: HighPerformanceCUDAZKAccelerator, ProductionCUDAZKAPI

✅ DOCUMENTATION ARCHIVE CONTENTS:
- MIGRATION_CHECKLIST.md: Step-by-step migration procedures
- basic_migration.py: Direct CUDA calls to abstraction layer examples
- api_migration.py: FastAPI endpoint migration examples
- config_migration.py: Configuration migration examples

✅ ROOT DIRECTORY CLEANUP: Removed legacy examples from production directory
- migration_examples/ moved to docs/archive/migration_examples/
- Root directory now contains only active production components
- Legacy migration examples preserved for historical reference

DIRECTORY STRUCTURE IMPROVEMENT:
📁 docs/archive/migration_examples/: Historical migration documentation
🏗️ Root Directory: Clean production structure with only active components
📚 Documentation Archive: Legacy content properly organized for reference

BENEFITS:
✅ Clean Production Directory: No legacy examples in root
✅ Historical Preservation: Migration examples preserved for reference
✅ Better Organization: Legacy content grouped in documentation archive
✅ Clear Separation: Active vs legacy content clearly distinguished

RESULT: Successfully moved legacy migration examples to docs/archive/migration_examples/ subdirectory, cleaning up the root directory while preserving historical migration documentation for future reference.

docs/archive/migration_examples/MIGRATION_CHECKLIST.md

@@ -0,0 +1,112 @@
+# GPU Acceleration Migration Checklist
+
+## ✅ Pre-Migration Preparation
+
+- [ ] Review existing CUDA-specific code
+- [ ] Identify all files that import CUDA modules
+- [ ] Document current CUDA usage patterns
+- [ ] Create backup of existing code
+- [ ] Test current functionality
+
+## ✅ Code Migration
+
+### Import Statements
+- [ ] Replace `from high_performance_cuda_accelerator import ...` with `from gpu_acceleration import ...`
+- [ ] Replace `from fastapi_cuda_zk_api import ...` with `from gpu_acceleration import ...`
+- [ ] Update all CUDA-specific imports
+
+### Function Calls
+- [ ] Replace `accelerator.field_add_cuda()` with `gpu.field_add()`
+- [ ] Replace `accelerator.field_mul_cuda()` with `gpu.field_mul()`
+- [ ] Replace `accelerator.multi_scalar_mul_cuda()` with `gpu.multi_scalar_mul()`
+- [ ] Update all CUDA-specific function calls
+
+### Initialization
+- [ ] Replace `HighPerformanceCUDAZKAccelerator()` with `GPUAccelerationManager()`
+- [ ] Replace `ProductionCUDAZKAPI()` with `create_gpu_manager()`
+- [ ] Add proper error handling for backend initialization
+
+### Error Handling
+- [ ] Add fallback handling for GPU failures
+- [ ] Update error messages to be backend-agnostic
+- [ ] Add backend information to error responses
+
+## ✅ Testing
+
+### Unit Tests
+- [ ] Update unit tests to use new interface
+- [ ] Test backend auto-detection
+- [ ] Test fallback to CPU
+- [ ] Test performance regression
+
+### Integration Tests
+- [ ] Test API endpoints with new backend
+- [ ] Test multi-backend scenarios
+- [ ] Test configuration options
+- [ ] Test error handling
+
+### Performance Tests
+- [ ] Benchmark new vs old implementation
+- [ ] Test performance with different backends
+- [ ] Verify no significant performance regression
+- [ ] Test memory usage
+
+## ✅ Documentation
+
+### Code Documentation
+- [ ] Update docstrings to be backend-agnostic
+- [ ] Add examples for new interface
+- [ ] Document configuration options
+- [ ] Update error handling documentation
+
+### API Documentation
+- [ ] Update API docs to reflect backend flexibility
+- [ ] Add backend information endpoints
+- [ ] Update performance monitoring docs
+- [ ] Document migration process
+
+### User Documentation
+- [ ] Update user guides with new examples
+- [ ] Document backend selection options
+- [ ] Add troubleshooting guide
+- [ ] Update installation instructions
+
+## ✅ Deployment
+
+### Configuration
+- [ ] Update deployment scripts
+- [ ] Add backend selection environment variables
+- [ ] Update monitoring for new metrics
+- [ ] Test deployment with different backends
+
+### Monitoring
+- [ ] Update monitoring to track backend usage
+- [ ] Add alerts for backend failures
+- [ ] Monitor performance metrics
+- [ ] Track fallback usage
+
+### Rollback Plan
+- [ ] Document rollback procedure
+- [ ] Test rollback process
+- [ ] Prepare backup deployment
+- [ ] Create rollback triggers
+
+## ✅ Validation
+
+### Functional Validation
+- [ ] All existing functionality works
+- [ ] New backend features work correctly
+- [ ] Error handling works as expected
+- [ ] Performance is acceptable
+
+### Security Validation
+- [ ] No new security vulnerabilities
+- [ ] Backend isolation works correctly
+- [ ] Input validation still works
+- [ ] Error messages don't leak information
+
+### Performance Validation
+- [ ] Performance meets requirements
+- [ ] Memory usage is acceptable
+- [ ] Scalability is maintained
+- [ ] Resource utilization is optimal