chore(task-board): mothball it; superseded by the High Seat and ledger

Operator ruling 2026-09-24. On ana-docker the stack is `docker compose
down`: the container is removed and port 7878 is closed. Kept for revival:
- the data dir /opt/docker/conf/task-board/data (tasks.db, last written
  2026-09-11)
- the task-board:local image
- stacks/task-board/ and the host's compose + .env

The Uptime Kuma monitor (id 3) was deleted before the stop so it could
not page, and its row is removed from monitors.yaml. Homepage drops the
card on its own, since it reads the container's labels.

Hooks: the container log showed no hook POSTs in 30 days. The only
traffic was open browser tabs holding /events, and the plugin was already
uninstalled on nh3-dev. Removed the paragraph that told sessions to call
task_* tools (CLAUDE.md, and the fork-fleet.sh template that seeds new
repos), the vestigial TASK_BOARD_SESSION env in .claude/settings.json, and
the listings in README and FLEETTOOLS.

docs/fleettools/observability.md

@@ -7,7 +7,7 @@
 | **Dozzle** | `http://10.250.50.70:8088` | container logs, ana-docker + ana-ml2 |
 | **Uptime Kuma** | `http://10.0.50.45:3001` | ESH-side service monitoring |
 | **Backrest** | `http://10.250.50.70:9898` | restic snapshot browse / restore |
-| **task-board** | `http://10.250.50.70:7878` | what an assistant session is working on right now |
+| ~~task-board~~ | — | **mothballed 2026-09-24**; what a session is working on now lives on the High Seat (`http://10.100.10.50:8770`) |
 | Dockge (per host) | `<host>:5001` | compose UI on ana-docker, ana-ml2, esh-docker-vm, irv-ml1, nh3-docker |
 | PBS | `10.250.50.90:8007` (primary) · `10.100.50.90:8007` (DR) | VM/LXC image backups |