feat(core-realtime): scaffold realtime optional core

Generator-emitted scaffold (pnpm turbo gen core-package realtime) plus
the story-00-precedent coverage repairs (coverage provider devDep,
symbols.ts exclude + tested allowlist mirror) and three minimal tests
covering generator-emitted realtime code the template suite misses.
Squash of 31d85e0 + review-fix cf11b38.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/core-realtime/src/socket-io-realtime-broadcaster.ts

@@ -0,0 +1,17 @@
+import type { Server as IOServer } from "socket.io";
+import type { z } from "zod";
+import { channelRoom } from "./channel-room";
+import type { IRealtimeBroadcaster } from "./realtime-broadcaster.interface";
+import type { RealtimeChannelDescriptor } from "./realtime-channel";
+
+export class SocketIORealtimeBroadcaster implements IRealtimeBroadcaster {
+  constructor(private readonly io: IOServer) {}
+
+  async broadcast<T>(
+    descriptor: RealtimeChannelDescriptor<string, z.ZodType<T>>,
+    payload: T,
+  ): Promise<void> {
+    descriptor.schema.parse(payload);
+    this.io.to(channelRoom(descriptor.name)).emit(descriptor.name, payload);
+  }
+}