feat: add incremental log scanning with resumable byte offsets

Track last processed byte offset per log file so scans only read new
entries, add --full flag to force a rescan, and persist state atomically.

app/copyparty.py

@@ -164,6 +164,8 @@ def main() -> None:
         COPYPARTY_LOG_PATH, COPYPARTY_REPORT_DIR)
     parser.add_argument("--min-denied", type=int, default=DEFAULT_MIN_DENIED,
                         help=f"minimum denied hits before flagging (default: {DEFAULT_MIN_DENIED})")
+    parser.add_argument("--full", action="store_true",
+                        help="rescan all logs from the start (ignore incremental state)")
     args = parser.parse_args()
 
     CopypartyAnalyzer(
@@ -171,6 +173,7 @@ def main() -> None:
         report_dir=args.report_dir,
         top=args.top,
         quiet=args.quiet,
+        full=args.full,
         min_denied=args.min_denied,
     ).run()