feat: Client-published events + realtime presence

- POST /projects/:id/events accepts client-authored events restricted to
  the custom.* namespace — system types can't be spoofed. They flow
  through the same publishEvent fan-out: realtime, webhooks, and
  event_pattern functions all fire.
- Presence: subscribe/unsubscribe bumps a per-project count and
  broadcasts presence.update {online} to the realtime stream only —
  deliberately not through publishEvent so webhooks and "*" functions
  don't fire on connect noise. GET …/realtime/presence reads the count.
- @primora/client gains publish() and presence(); CLI gains events:send.

Verified live: presence 0->1 on subscribe, presence.update frame
delivered, custom event delivered to SSE + fired a custom.* function,
spoofed document.created rejected 400.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

packages/api-client/src/generated/models/PublishEventRequest.ts

@@ -0,0 +1,15 @@
+/* generated using openapi-typescript-codegen -- do not edit */
+/* istanbul ignore file */
+/* tslint:disable */
+/* eslint-disable */
+export type PublishEventRequest = {
+    /**
+     * Event type in the custom.* namespace — realtime subscribers, matching webhooks, and event_pattern functions all fire.
+     */
+    type: string;
+    /**
+     * Arbitrary JSON payload carried to subscribers.
+     */
+    data?: Record<string, any>;
+};
+