docs: correct comments that contradict the code

- part id is 0-indexed in both --help and the loader docstring, matching the matrix
- daily release cron comment said 6:00pm while the expression fires at 06:00 UTC

Generated-by: Claude Opus 5 <noreply@anthropic.com>

src/adsb/compress_adsb_to_aircraft_data.py

@@ -141,7 +141,7 @@ def load_parquet_part(part_id: int, date: str) -> pl.DataFrame:
     """Load a single parquet part file for a date.
     
     Args:
-        part_id: Part ID (e.g., 1, 2, 3)
+        part_id: Part ID (0-indexed, e.g. 0, 1, 2, 3)
         date: Date string in YYYY-MM-DD format
     
     Returns:

src/adsb/process_icao_chunk.py

@@ -116,7 +116,7 @@ from pathlib import Path
 
 def main():
     parser = argparse.ArgumentParser(description="Process a single archive part for a day")
-    parser.add_argument("--part-id", type=int, required=True, help="Part ID (1-indexed)")
+    parser.add_argument("--part-id", type=int, required=True, help="Part ID (0-indexed)")
     parser.add_argument("--date", type=str, required=True, help="Date in YYYY-MM-DD format")
     args = parser.parse_args()