Update auth references from JWT to session tokens

- Remove previous_token_grace_until from RotateApiTokenResponse
- Update client/async_client docstrings
- Update CLI help text and README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

elydora/client.py

@@ -50,7 +50,7 @@ class ElydoraClient:
         base_url: API base URL.
         ttl_ms: Time-to-live for operations in milliseconds.
         max_retries: Maximum number of retries on transient failures.
-        token: Optional JWT bearer token for authenticated endpoints.
+        token: Optional API token for authenticated endpoints.
     """
 
     def __init__(
@@ -181,7 +181,7 @@ class ElydoraClient:
 
     @staticmethod
     def login(base_url: str, email: str, password: str) -> AuthLoginResponse:
-        """Authenticate and receive a JWT."""
+        """Authenticate and receive a session token."""
         url = f"{base_url.rstrip('/')}/v1/auth/login"
         body = {"email": email, "password": password}
         resp = requests.post(url, json=body, headers={"Content-Type": "application/json"}, timeout=30)