Space watch URL fetches with FETCH_GAP_SECONDS (default 1s)

Same tick previously fired every due watch back-to-back (burst of N requests,
worst right after a restart when all watches are due at once). Now each watch
URL fetch is followed by a pause of FETCH_GAP_SECONDS (float, default 1, env
tunable; 0 disables) on both success and failure paths.

Also thread kw_fk_col into load_ignored_keywords() inside
send_pending_notifications() so the physical-FK lookup (445040a) actually takes
effect instead of silently falling back to the watch Link column.

docker-compose.yml

@@ -18,6 +18,7 @@ services:
       TELEGRAM_BOT_TOKEN: ${TELEGRAM_BOT_TOKEN}
       TELEGRAM_CHAT_ID: ${TELEGRAM_CHAT_ID}
       TICK_SECONDS: ${TICK_SECONDS:-60}
+      FETCH_GAP_SECONDS: ${FETCH_GAP_SECONDS:-1}
       HEALTH_STALE_SECONDS: ${HEALTH_STALE_SECONDS:-600}
       TZ: Asia/Kuala_Lumpur
     volumes: