Increase history retention to 20, run scrapers every 4 hours

- generate_status.py: raise --keep default from 5 to 20 entries
- build/crontab: change schedule from 06:00/18:00 to every 4 hours (*/4)
  covers 6 runs/day ≈ 3.3 days of history at default retention

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

build/crontab

@@ -1 +1 @@
-0 6,18 * * * cd /app && bash /app/run_all.sh >> /proc/1/fd/1 2>> /proc/1/fd/2
+0 */4 * * * cd /app && bash /app/run_all.sh >> /proc/1/fd/1 2>> /proc/1/fd/2

generate_status.py

@@ -84,8 +84,8 @@ def main():
                         help="ISO timestamp of scrape start (default: now)")
     parser.add_argument("--duration", dest="duration", type=int, default=None,
                         help="Run duration in seconds")
-    parser.add_argument("--keep", dest="keep", type=int, default=5,
+    parser.add_argument("--keep", dest="keep", type=int, default=20,
-                        help="Number of history entries to keep (default: 5, 0=unlimited)")
+                        help="Number of history entries to keep (default: 20, 0=unlimited)")
     args = parser.parse_args()
 
     start_time = args.start_time or datetime.now().isoformat(timespec="seconds")