feat: add auth token storage module

nanobot/auth/__init__.py

@@ -0,0 +1,56 @@
+"""Token storage for nanobot auth."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from dataclasses import dataclass
+
+
+@dataclass
+class AuthInfo:
+    token: str
+    server_url: str
+    expires_at: float | None = None
+
+
+def _auth_file_path() -> Path:
+    return Path.home() / ".nanobot" / "auth.json"
+
+
+def load_auth() -> AuthInfo | None:
+    """Load saved auth info from disk."""
+    path = _auth_file_path()
+    if not path.exists():
+        return None
+    try:
+        data = json.loads(path.read_text(encoding="utf-8"))
+        return AuthInfo(
+            token=data["token"],
+            server_url=data["server_url"],
+            expires_at=data.get("expires_at"),
+        )
+    except (json.JSONDecodeError, KeyError):
+        return None
+
+
+def save_auth(info: AuthInfo) -> None:
+    """Save auth info to disk."""
+    path = _auth_file_path()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    data = {
+        "token": info.token,
+        "server_url": info.server_url,
+    }
+    if info.expires_at is not None:
+        data["expires_at"] = info.expires_at
+    path.write_text(json.dumps(data, indent=2), encoding="utf-8")
+
+
+def delete_auth() -> bool:
+    """Delete saved auth info. Returns True if file was deleted."""
+    path = _auth_file_path()
+    if path.exists():
+        path.unlink()
+        return True
+    return False