refactor: organize scripts/, remove stale root dirs, clean up structure

scripts/ reorganization:
- Sort 14 loose root scripts into subfolders:
  blockchain/ (genesis, proposer, mock chain, testnet BTC)
  dev/ (CLI wrapper, dev services, OpenAPI gen, systemd setup, domain proxy)
  ops/ (coordinator proxy, remote tunnel)
  gpu/ (miner workflow)
- Merge scripts/testing/ into scripts/test/ (eliminate duplicate folder)
- Create scripts/examples/ for usage demos and simulations

Root-level cleanup:
- Move home/ (12 simulation scripts) → scripts/examples/
- Move dev-utils/ (2 files) → scripts/dev/
- Move protocols/receipts/sample → tests/fixtures/
- Delete stale src/ (duplicate of apps/blockchain-node/src/)
- Remove empty home/, dev-utils/, protocols/ directories

Documentation updates:
- Update docs/6_architecture/8_codebase-structure.md tree and table
- Update root README.md tree to reflect new structure

scripts/test/test_model_validation.py

@@ -0,0 +1,57 @@
+#!/usr/bin/env python3
+"""
+Test the BlockImportRequest model
+"""
+
+from pydantic import BaseModel, Field
+from typing import Dict, Any, List, Optional
+
+class TransactionData(BaseModel):
+    tx_hash: str
+    sender: str
+    recipient: str
+    payload: Dict[str, Any] = Field(default_factory=dict)
+
+class BlockImportRequest(BaseModel):
+    height: int = Field(gt=0)
+    hash: str
+    parent_hash: str
+    proposer: str
+    timestamp: str
+    tx_count: int = Field(ge=0)
+    state_root: Optional[str] = None
+    transactions: List[TransactionData] = Field(default_factory=list)
+
+# Test creating the request
+test_data = {
+    "height": 1,
+    "hash": "0xtest",
+    "parent_hash": "0x00",
+    "proposer": "test",
+    "timestamp": "2026-01-29T10:20:00",
+    "tx_count": 1,
+    "transactions": [{
+        "tx_hash": "0xtx123",
+        "sender": "0xsender",
+        "recipient": "0xrecipient",
+        "payload": {"test": "data"}
+    }]
+}
+
+print("Test data:")
+print(test_data)
+
+try:
+    request = BlockImportRequest(**test_data)
+    print("\n✅ Request validated successfully!")
+    print(f"Transactions count: {len(request.transactions)}")
+    if request.transactions:
+        tx = request.transactions[0]
+        print(f"First transaction:")
+        print(f"  tx_hash: {tx.tx_hash}")
+        print(f"  sender: {tx.sender}")
+        print(f"  recipient: {tx.recipient}")
+except Exception as e:
+    print(f"\n❌ Validation failed: {e}")
+    import traceback
+    traceback.print_exc()