docs: update documentation links to use relative paths and add system flow references

- Replace absolute aitbc.bubuit.net URLs with relative paths in documentation pages
- Update markdown documentation links from /main/ to /master/ branch
- Add system flow diagram references to component documentation pages
- Remove redundant "Also available in Markdown" notices from HTML docs
- Update Font Awesome CDN link in index.html
- Simplify quick links section and remove unused tutorial/video guide plac

tests/mock_blockchain_node.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""
+Mock blockchain node server for testing purposes.
+Implements the minimal API endpoints required by the test suite.
+"""
+
+import json
+import threading
+import time
+from typing import Dict, Any
+
+from fastapi import FastAPI
+from fastapi.responses import JSONResponse
+import uvicorn
+
+# Create FastAPI app
+app = FastAPI(title="Mock Blockchain Node", version="0.1.0")
+
+# Mock state
+mock_chain_state = {
+    "height": 100,
+    "hash": "0xabcdef1234567890",
+    "balances": {
+        "aitbc1alice00000000000000000000000000000000000": 1000,
+        "aitbc1bob0000000000000000000000000000000000000": 500,
+        "aitbc1charl0000000000000000000000000000000000": 100
+    },
+    "transactions": []
+}
+
+@app.get("/openapi.json")
+async def openapi():
+    """Return OpenAPI spec"""
+    return {
+        "openapi": "3.0.0",
+        "info": {
+            "title": "AITBC Blockchain API",
+            "version": "0.1.0"
+        },
+        "paths": {}
+    }
+
+@app.get("/rpc/head")
+async def get_chain_head():
+    """Get current chain head"""
+    return JSONResponse(mock_chain_state)
+
+@app.get("/rpc/getBalance/{address}")
+async def get_balance(address: str):
+    """Get balance for an address"""
+    balance = mock_chain_state["balances"].get(address, 0)
+    return JSONResponse({"balance": balance})
+
+@app.post("/rpc/admin/mintFaucet")
+async def mint_faucet(request: Dict[str, Any]):
+    """Mint tokens to an address (devnet only)"""
+    address = request.get("address")
+    amount = request.get("amount", 0)
+    
+    if address in mock_chain_state["balances"]:
+        mock_chain_state["balances"][address] += amount
+    else:
+        mock_chain_state["balances"][address] = amount
+    
+    return JSONResponse({"success": True, "new_balance": mock_chain_state["balances"][address]})
+
+@app.post("/rpc/sendTx")
+async def send_transaction(request: Dict[str, Any]):
+    """Send a transaction"""
+    # Generate mock transaction hash
+    tx_hash = f"0x{hash(str(request)) % 1000000000000000000000000000000000000000000000000000000000000000:x}"
+    
+    # Add to transactions list
+    mock_chain_state["transactions"].append({
+        "hash": tx_hash,
+        "type": request.get("type", "TRANSFER"),
+        "sender": request.get("sender"),
+        "timestamp": time.time()
+    })
+    
+    return JSONResponse({"tx_hash": tx_hash, "status": "pending"})
+
+@app.get("/health")
+async def health():
+    """Health check endpoint"""
+    return JSONResponse({"status": "ok", "height": mock_chain_state["height"]})
+
+def run_mock_server(port: int):
+    """Run the mock server on specified port"""
+    uvicorn.run(app, host="127.0.0.1", port=port, log_level="warning")
+
+if __name__ == "__main__":
+    import sys
+    port = int(sys.argv[1]) if len(sys.argv) > 1 else 8081
+    print(f"Starting mock blockchain node on port {port}")
+    run_mock_server(port)