```

chore: refactor logging module, update genesis timestamp, remove model relationships, and reorganize routers

- Rename logging.py to logger.py and update import paths in poa.py and main.py
- Update devnet genesis timestamp to 1766828620
- Remove SQLModel Relationship declarations from Block, Transaction, and Receipt models
- Add SessionDep type alias and get_session dependency in coordinator-api deps
- Reorganize coordinator-api routers: replace explorer/registry with exchange, users, marketplace

apps/blockchain-node/src/aitbc_chain/logger.py

@@ -0,0 +1,71 @@
+from __future__ import annotations
+
+import logging
+from datetime import datetime
+from typing import Any, Optional
+
+import json
+
+
+class JsonFormatter(logging.Formatter):
+    RESERVED = {
+        "name",
+        "msg",
+        "args",
+        "levelname",
+        "levelno",
+        "pathname",
+        "filename",
+        "module",
+        "exc_info",
+        "exc_text",
+        "stack_info",
+        "lineno",
+        "funcName",
+        "created",
+        "msecs",
+        "relativeCreated",
+        "thread",
+        "threadName",
+        "process",
+        "processName",
+    }
+
+    def format(self, record: logging.LogRecord) -> str:  # type: ignore[override]
+        payload: dict[str, Any] = {
+            "timestamp": datetime.utcnow().isoformat() + "Z",
+            "level": record.levelname,
+            "logger": record.name,
+            "message": record.getMessage(),
+        }
+
+        for key, value in record.__dict__.items():
+            if key in self.RESERVED or key.startswith("_"):
+                continue
+            payload[key] = value
+
+        if record.exc_info:
+            payload["exc_info"] = self.formatException(record.exc_info)
+        if record.stack_info:
+            payload["stack"] = record.stack_info
+
+        return json.dumps(payload, default=str)
+
+
+def configure_logging(level: Optional[str] = None) -> None:
+    log_level = getattr(logging, (level or "INFO").upper(), logging.INFO)
+    root = logging.getLogger()
+    if root.handlers:
+        return
+
+    handler = logging.StreamHandler()
+    formatter = JsonFormatter()
+    handler.setFormatter(formatter)
+    root.addHandler(handler)
+    root.setLevel(log_level)
+
+
+def get_logger(name: str) -> logging.Logger:
+    if not logging.getLogger().handlers:
+        configure_logging()
+    return logging.getLogger(name)