feat(turbo-gen): templates for gen realtime handler

turbo/generators/templates/realtime/handler/handler.ts.hbs

@@ -0,0 +1,13 @@
+// packages/{{kebabCase feature}}/src/realtime/handlers/on-{{kebabCase channelSlug}}.handler.ts
+import type { {{pascalCase channelSlug}}Payload } from "../{{kebabCase channelSlug}}.channel";
+import type { RealtimeContext } from "@repo/core-realtime";
+
+export type IOn{{pascalCase channelSlug}}Handler = ReturnType<typeof on{{pascalCase channelSlug}}Handler>;
+
+export const on{{pascalCase channelSlug}}Handler =
+  () =>
+  async (_input: {{pascalCase channelSlug}}Payload, _ctx: RealtimeContext): Promise<void> => {
+    // TODO: implement the reaction. Inject deps via the factory's constructor
+    // and use them here. The handler is wrapped in span+capture at bind time,
+    // so just throwing on failure is the right shape.
+  };