docs(workflows): fix stale FanOutStep docstring claiming sequential-only execution (#3639)

The FanOutStep class docstring stated that fan-out execution is
"currently sequential" and that `max_concurrency` is "accepted but not
enforced". That has been inaccurate since #3224, which added a bounded
thread-pool concurrency path to `WorkflowEngine._run_fan_out` that honors
`max_concurrency > 1`.

Update the docstring to match the engine's own `_run_fan_out` docstring:
`max_concurrency <= 1` (the default) runs items sequentially, while `> 1`
runs up to that many items concurrently on a bounded thread pool.
Docstring-only; no behavior change.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: jawwad-ali

src/specify_cli/workflows/steps/fan_out/__init__.py

@@ -12,9 +12,10 @@ class FanOutStep(StepBase):
     """Dispatch a step template for each item in a collection.
 
     The engine executes the nested ``step:`` template once per item,
-    setting ``context.item`` for each iteration.  Execution is
-    currently sequential; ``max_concurrency`` is accepted but not
-    enforced.
+    setting ``context.item`` for each iteration.  ``max_concurrency``
+    controls parallelism: ``<= 1`` (the default) runs items
+    sequentially, while ``> 1`` runs up to that many items concurrently
+    on a bounded thread pool (see ``WorkflowEngine._run_fan_out``).
     """
 
     type_key = "fan-out"