feat(gui): generic command flow node and the conversation.chat.commandview keyed slot

The FoldAdapter folds the log-only command/run + command/done pair (paired
by commandId) into a CommandNode outside the surface fold and merges the
nodes into the flow by seq; cross-window cuts soft-fall like tool pairs (a
done-only window builds the node from the done, a run with no done renders
as still executing). ChatView renders command nodes through the new keyed
'conversation.chat.commandview' hole (key = command name) with
GenericCommandCard — a stripped-down GenericToolCard showing the command
line and outcome text — as the render-site fallback, so any slash command
renders durably with zero registration and survives refresh, other tabs,
and resume via the mux-broadcast events.

packages/client/runtime/tests/event-script.ts

@@ -42,6 +42,10 @@ export const ev = {
     at(seq, { type: 'turn/end', data: { turn, reason: { kind: reason } } }),
   todoWrite: (seq: number, todos: { content: string; status: 'pending' | 'in_progress' | 'completed' }[]): SessionEvent =>
     at(seq, { type: 'todo/write', data: { todos } }),
+  commandRun: (seq: number, commandId: string, name: string, line: string): SessionEvent =>
+    at(seq, { type: 'command/run', data: { commandId, name, line, source: { kind: 'user' } } }),
+  commandDone: (seq: number, commandId: string, kind: 'success' | 'error' = 'success', text?: string): SessionEvent =>
+    at(seq, { type: 'command/done', data: { commandId, kind, ...text === undefined ? {} : { text } } }),
 }
 
 /** One complete plain turn (turn/start → user → step → assistant → turn/end), 6 events from startSeq. */