feat: wire channel mode runtime config and docs

plugin/core/channel-modes.ts

@@ -1,10 +1,7 @@
-export type ChannelMode = "normal" | "multi-message";
+import type { ChannelRuntimeMode, ChannelRuntimeState } from "../rules.js";
 
-export type ChannelModesState = {
-  mode: ChannelMode;
-  shuffling: boolean;
-  lastShuffledAt?: number;
-};
+export type ChannelMode = ChannelRuntimeMode;
+export type ChannelModesState = ChannelRuntimeState;
 
 const channelStates = new Map<string, ChannelModesState>();
 
@@ -48,4 +45,4 @@ export function markLastShuffled(channelId: string): void {
   const state = getChannelState(channelId);
   state.lastShuffledAt = Date.now();
   channelStates.set(channelId, state);
-}
+}