docs: note Opus 4.8 Workflows as orthogonal top-level fan-out

The nested-subagent-dispatch constraint is unchanged in Opus 4.8.
Workflows added a top-level fan-out mechanism alongside it, but a
workflow's spawned agents still cannot spawn further agents. Record
this in both the design rationale and the README capability list so a
future reader does not read the plugin as unaware of Workflows.

README.md

@@ -45,7 +45,8 @@ This repo (the **plugin**) carries everything that is universal:
   / NEEDS_CONTEXT`
 - Working-tree-as-quarantine and only-orchestrator-commits
 - main HEAD sacrosanct
-- No nested subagent dispatch (Claude Code platform constraint)
+- No nested subagent dispatch (Claude Code platform constraint;
+  Opus 4.8 Workflows fan out at the top level but do not lift it)
 - No orphan agents
 
 Your project carries a small **profile** that fills the slots:

docs/design.md

@@ -44,7 +44,11 @@ The plugin owns:
   main moves forward only via orchestrator commits.
 - **No nested subagent dispatch** — a hard Claude Code
   platform constraint; the implement-orchestrator runs phases
-  as sequential role-switches inside its own context.
+  as sequential role-switches inside its own context. Opus 4.8
+  added Workflows as an orthogonal top-level fan-out mechanism
+  but did not lift this constraint — a workflow script
+  orchestrates from the top level, yet the agents it spawns
+  still cannot spawn further agents.
 - **No orphan agents** — every agent lives under the skill
   that dispatches it.
 - **Output budget discipline** — agents have word budgets on