docs(kanban): backfill multi-board refs in reference docs (#19704)

Followup to #19653. The feature PR updated the Kanban user guide but
missed four other pages that document the same surface. Caught when
Teknium asked 'did you add docs to the guide and any other kanban
related docs around this?'.

- reference/cli-commands.md: rewrite the `hermes kanban` section to
  document the `--board <slug>` global flag, the `boards`
  subcommand group (list/create/switch/show/rename/rm), board
  resolution order, and worked examples. Also fills in the
  `create` / `complete` flag lists that had drifted from the
  current CLI (`--summary`, `--metadata`, `--triage`,
  `--idempotency-key`, `--max-runtime`, `--skill`).
- reference/environment-variables.md: add `HERMES_KANBAN_BOARD`
  row, update `HERMES_KANBAN_DB` precedence note.
- reference/slash-commands.md: add `/kanban boards ...` and
  `/kanban --board <slug> ...` to the two `/kanban` rows (CLI
  table + gateway table).
- features/kanban-tutorial.md: the walkthrough uses the `default`
  board, so just a note pointing readers at the overview's Boards
  section if they want multiple queues, plus the corrected per-board
  DB path.

Skill docs (devops-kanban-orchestrator, -worker) intentionally not
updated: those are agent-facing lifecycle playbooks and boards are
transparent to workers (HERMES_KANBAN_BOARD env var pins the DB
automatically), so there's nothing new for a worker to know.

website/docs/reference/slash-commands.md

@@ -70,7 +70,7 @@ Type `/` in the CLI to open the autocomplete menu. Built-in commands are case-in
 | `/skills` | Search, install, inspect, or manage skills from online registries |
 | `/cron` | Manage scheduled tasks (list, add/create, edit, pause, resume, run, remove) |
 | `/curator` | Background skill maintenance — `status`, `run`, `pin`, `archive`. See [Curator](/docs/user-guide/features/curator). |
-| `/kanban <action>` | Drive the multi-profile collaboration board without leaving chat. Full `hermes kanban` surface is available: `/kanban list`, `/kanban show t_abc`, `/kanban create "title" --assignee X`, `/kanban comment t_abc "text"`, `/kanban unblock t_abc`, `/kanban dispatch`, etc. See [Kanban slash command](/docs/user-guide/features/kanban#kanban-slash-command). |
+| `/kanban <action>` | Drive the multi-profile, multi-project collaboration board without leaving chat. Full `hermes kanban` surface is available: `/kanban list`, `/kanban show t_abc`, `/kanban create "title" --assignee X`, `/kanban comment t_abc "text"`, `/kanban unblock t_abc`, `/kanban dispatch`, etc. Multi-board support included: `/kanban boards list`, `/kanban boards create <slug>`, `/kanban boards switch <slug>`, `/kanban --board <slug> <action>`. See [Kanban slash command](/docs/user-guide/features/kanban#kanban-slash-command). |
 | `/reload-mcp` (alias: `/reload_mcp`) | Reload MCP servers from config.yaml |
 | `/reload` | Reload `.env` variables into the running session (picks up new API keys without restarting) |
 | `/plugins` | List installed plugins and their status |
@@ -158,7 +158,7 @@ The messaging gateway supports the following built-in commands inside Telegram,
 | `/goal <text>` | Set a standing goal Hermes works toward across turns — our take on the Ralph loop. A judge model checks after each turn; if not done, Hermes auto-continues until it is, you pause/clear it, or the turn budget (default 20) is hit. Subcommands: `/goal status`, `/goal pause`, `/goal resume`, `/goal clear`. Safe to run mid-agent for status/pause/clear; setting a new goal requires `/stop` first. See [Persistent Goals](/docs/user-guide/features/goals). |
 | `/footer [on\|off\|status]` | Toggle the runtime-metadata footer on final replies (shows model, tool counts, timing). |
 | `/curator [status\|run\|pin\|archive]` | Background skill maintenance controls. |
-| `/kanban <action>` | Drive the multi-profile collaboration board from chat — identical argument surface to the CLI. Bypasses the running-agent guard, so `/kanban unblock t_abc`, `/kanban comment t_abc "…"`, `/kanban list --mine`, etc. work mid-turn. `/kanban create …` auto-subscribes the originating chat to the new task's terminal events. See [Kanban slash command](/docs/user-guide/features/kanban#kanban-slash-command). |
+| `/kanban <action>` | Drive the multi-profile, multi-project collaboration board from chat — identical argument surface to the CLI. Bypasses the running-agent guard, so `/kanban unblock t_abc`, `/kanban comment t_abc "…"`, `/kanban list --mine`, `/kanban boards switch <slug>`, etc. work mid-turn. `/kanban create …` auto-subscribes the originating chat to the new task's terminal events. See [Kanban slash command](/docs/user-guide/features/kanban#kanban-slash-command). |
 | `/reload-mcp` (alias: `/reload_mcp`) | Reload MCP servers from config. |
 | `/yolo` | Toggle YOLO mode — skip all dangerous command approval prompts. |
 | `/commands [page]` | Browse all commands and skills (paginated). |