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- Legacy migration examples preserved for historical reference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/config_migration.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+"""
+Configuration Migration Example
+
+Shows how to migrate configuration to use the new abstraction layer.
+"""
+
+# BEFORE (CUDA-specific config)
+# cuda_config = {
+#     "lib_path": "./liboptimized_field_operations.so",
+#     "device_id": 0,
+#     "memory_limit": 8*1024*1024*1024
+# }
+
+# AFTER (Backend-agnostic config)
+from gpu_acceleration import ZKOperationConfig, GPUAccelerationManager, ComputeBackend
+
+# Configuration for any backend
+config = ZKOperationConfig(
+    batch_size=2048,
+    use_gpu=True,
+    fallback_to_cpu=True,
+    timeout=60.0,
+    memory_limit=8*1024*1024*1024  # 8GB
+)
+
+# Create manager with specific backend
+gpu = GPUAccelerationManager(backend=ComputeBackend.CUDA, config=config)
+gpu.initialize()
+
+# Or auto-detect with config
+from gpu_acceleration import create_gpu_manager
+gpu = create_gpu_manager(
+    backend="cuda",  # or None for auto-detect
+    batch_size=2048,
+    fallback_to_cpu=True,
+    timeout=60.0
+)