fix(kanban): text dispatch output and both "dispatcher stuck" warnings name the hold reason

`hermes kanban dispatch` (plain output), the standalone daemon's stuck warning
and the gateway's embedded dispatcher stuck warning all reported a bare
`Spawned: 0` / "0 workers spawned" while the respawn guard held every ready
card — the reason existed only as a `respawn_guarded` task event visible via
`hermes kanban tail`. Operators watching the gateway health warning for 73+
ticks (#111910) had nothing to act on.

- `kanban_db_dispatch.describe_suppression()` renders the guard reasons per
  task plus rate_limited / skipped_locked / memory_pressure for one or more
  DispatchResults, so the CLI daemon and gateway warnings share one wording:
  `Last tick held back: active_pr=1, memory_pressure=elevated.`
- plain `dispatch` output prints `Guarded (<reason>): <task id>` and the
  tick-level holds, mirroring the JSON fields.
- kanban docs: how to see why a ready card is not spawning.

Co-authored-by: Steven Saehrig <trac3r726@users.noreply.github.com>

Part of #111910

gateway/kanban_watchers.py

@@ -272,6 +272,7 @@ class GatewayKanbanWatchersMixin:
         # broken PATH, missing venv, or credential loss.
         bad_ticks = 0
         last_warn_at = 0
+        results: Optional[list] = None
         dispatcher = _KanbanDispatcher(_kb, settings)
 
         logger.info("kanban dispatcher: embedded in gateway (interval=%.1fs)", interval)
@@ -304,12 +305,13 @@ class GatewayKanbanWatchersMixin:
                     bad_ticks = bad_ticks + 1 if ready_pending and not any_spawned else 0
                 now = int(time.time())
                 if bad_ticks >= _HEALTH_WINDOW and now - last_warn_at >= 300:
+                    held = _kbd.describe_suppression(res for _slug, res in (results or []))
                     logger.warning(
                         "kanban dispatcher stuck: ready queue non-empty for "
-                        "%d consecutive ticks but 0 workers spawned. Check "
+                        "%d consecutive ticks but 0 workers spawned.%s Check "
                         "profile health (venv, PATH, credentials) and "
                         "`hermes kanban list --status ready`.",
-                        bad_ticks,
+                        bad_ticks, f" Last tick held back: {held}." if held else "",
                     )
                     last_warn_at = now
             except asyncio.CancelledError: