server: remove diff switch, always send diffs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/main.py

@@ -120,12 +120,6 @@ def main() -> None:
         help="Directory for rotating log files (overrides credentials file, default: ./logs)",
     )
     p.add_argument("-v", "--verbose", action="store_true", help="Enable debug logging")
-    p.add_argument(
-        "--diff",
-        action="store_true",
-        default=None,
-        help="Send diffs instead of full snapshots over the push server (overrides credentials file, default: off)",
-    )
     p.add_argument(
         "--dry",
         action="store_true",
@@ -176,9 +170,6 @@ def main() -> None:
         args.port = int(creds_data.get("port", 9999))
     if args.log_dir is None:
         args.log_dir = creds_data.get("log_dir", "./logs")
-    if args.diff is None:
-        args.diff = bool(creds_data.get("diff", False))
-
     if not args.dry and (not args.username or not args.password):
         p.error(
             "Username and password are required.  "