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/blockchain/assign_proposer.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python3
+"""
+Script to assign a proposer to a block by polling for it
+"""
+
+import httpx
+import json
+
+# Configuration
+COORDINATOR_URL = "http://localhost:8001"
+MINER_API_KEY = "${MINER_API_KEY}"
+MINER_ID = "localhost-gpu-miner"
+
+def assign_proposer_to_latest_block():
+    """Poll for the latest unassigned job to become the proposer"""
+    
+    # First register the miner
+    print("📝 Registering miner...")
+    register_response = httpx.post(
+        f"{COORDINATOR_URL}/v1/miners/register?miner_id={MINER_ID}",
+        headers={
+            "Content-Type": "application/json",
+            "X-Api-Key": MINER_API_KEY
+        },
+        json={
+            "capabilities": {
+                "gpu": {"model": "RTX 4060 Ti", "memory_gb": 16}
+            }
+        }
+    )
+    
+    if register_response.status_code != 200:
+        print(f"❌ Registration failed: {register_response.text}")
+        return
+    
+    print("✅ Miner registered")
+    
+    # Poll for a job
+    print("\n🔍 Polling for jobs...")
+    poll_response = httpx.post(
+        f"{COORDINATOR_URL}/v1/miners/poll",
+        headers={
+            "Content-Type": "application/json",
+            "X-Api-Key": MINER_API_KEY
+        },
+        json={"max_wait_seconds": 1}
+    )
+    
+    if poll_response.status_code == 200:
+        job = poll_response.json()
+        print(f"✅ Received job: {job['job_id']}")
+        print(f"   This job is now assigned to miner: {MINER_ID}")
+        
+        # Check the block
+        print("\n📦 Checking block...")
+        blocks_response = httpx.get(f"{COORDINATOR_URL}/v1/explorer/blocks")
+        
+        if blocks_response.status_code == 200:
+            blocks = blocks_response.json()
+            for block in blocks['items']:
+                if block['hash'] == job['job_id']:
+                    print(f"✅ Block updated!")
+                    print(f"   Height: {block['height']}")
+                    print(f"   Hash: {block['hash']}")
+                    print(f"   Proposer: {block['proposer']}")
+                    break
+    elif poll_response.status_code == 204:
+        print("ℹ️  No jobs available to poll")
+    else:
+        print(f"❌ Poll failed: {poll_response.text}")
+
+if __name__ == "__main__":
+    print("🎯 Assign Proposer to Latest Block")
+    print("=" * 40)
+    assign_proposer_to_latest_block()