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.

COMPOSE-SETUP.md

@@ -96,6 +96,7 @@ build context is the repo directory).
       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
 ```
@@ -108,6 +109,7 @@ build context is the repo directory).
 | `TELEGRAM_BOT_TOKEN` | *(required)* | @carousellFoundBot token (xref `SECRETS.md`). |
 | `TELEGRAM_CHAT_ID` | *(required)* | `5648309582` — @MrFullStackDev. |
 | `TICK_SECONDS` | `60` | Scheduler granularity: heartbeat + watch-list reload interval. |
+| `FETCH_GAP_SECONDS` | `1` | Minimum pause (s) between watch URL fetches within one tick — prevents request bursts (default 1; set `0` to disable). |
 | `HEALTH_STALE_SECONDS` | `600` | Docker healthcheck tolerance: if last tick older than this → unhealthy. |
 | `TZ` | `Asia/Kuala_Lumpur` | Container clock (mostly cosmetic; timestamps are written in UTC deliberately for NocoDB). |