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>

apps/backend/internal/handlers/events.go

@@ -0,0 +1,44 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+)
+
+// publishEvent accepts a client-authored domain event (custom.* namespace)
+// and fans it out through the standard publishEvent path — realtime
+// subscribers, matching webhooks, and event_pattern functions all fire.
+func (h *HTTPHandler) publishEvent(c *gin.Context) {
+	actor, projectID, ok := h.actorAndProject(c)
+	if !ok {
+		return
+	}
+	var body struct {
+		Type string         `json:"type" validate:"required"`
+		Data map[string]any `json:"data"`
+	}
+	if !h.bindAndValidate(c, &body) {
+		return
+	}
+	if err := h.Platform.PublishProjectEvent(c.Request.Context(), actor, projectID, body.Type, body.Data); err != nil {
+		h.handleError(c, err)
+		return
+	}
+	c.JSON(http.StatusAccepted, gin.H{"published": body.Type})
+}
+
+// realtimePresence returns the count of clients currently subscribed to the
+// project's realtime stream.
+func (h *HTTPHandler) realtimePresence(c *gin.Context) {
+	actor, projectID, ok := h.actorAndProject(c)
+	if !ok {
+		return
+	}
+	n, err := h.Platform.Presence(c.Request.Context(), actor, projectID)
+	if err != nil {
+		h.handleError(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"online": n})
+}

apps/backend/internal/handlers/http.go

@@ -92,6 +92,7 @@ func (h *HTTPHandler) Register(router *gin.Engine) {
 	api.POST("/projects/:projectID/functions/:functionID/invoke", h.invokeFunction)
 	api.GET("/projects/:projectID/functions/:functionID/runs", h.listFunctionRuns)
 	api.GET("/projects/:projectID/events", h.listEvents)
+	api.POST("/projects/:projectID/events", h.publishEvent)
 	api.GET("/projects/:projectID/issues", h.listIssues)
 	api.GET("/projects/:projectID/components", h.listComponents)
 	api.DELETE("/projects/:projectID/components/:componentID", h.deleteComponent)
@@ -139,6 +140,7 @@ func (h *HTTPHandler) Register(router *gin.Engine) {
 	api.PUT("/projects/:projectID/alerts/:ruleID", h.updateAlertRule)
 	api.DELETE("/projects/:projectID/alerts/:ruleID", h.deleteAlertRule)
 	api.GET("/projects/:projectID/realtime/stream", h.realtimeStream)
+	api.GET("/projects/:projectID/realtime/presence", h.realtimePresence)
 	api.GET("/buckets/:bucketID/objects", h.listObjects)
 	api.POST("/buckets/:bucketID/objects", h.uploadObject)
 	api.POST("/buckets/:bucketID/object-copies", h.copyObject)