Show an event's entrypoint and request headers (closes #389)

An expanded event in the event log and the event's own page now show
the entrypoint the event arrived at (its description, "Entrypoint"
when it has none, or "deleted entrypoint"; never its URL) and the
full request headers, one per line, sorted by name. Both pages draw
them through one shared template, event_request.html. The event
columns now load entrypoint_id and headers, and the webhook's
entrypoints are read once per page.

Model: opus-5-5

internal/handlers/source_management.go

@@ -1240,7 +1240,8 @@ func (h *Handlers) loadEventsWithDeliveries(
 }
 
 // eventLogViews projects loaded events for rendering, each with
-// its deliveries and how many times it has been resubmitted. Like
+// its deliveries, how many times it has been resubmitted and the
+// entrypoint it arrived at. Like
 // loadEventsWithDeliveries, it reports false once it has answered
 // the request with an error.
 func (h *Handlers) eventLogViews(
@@ -1293,11 +1294,25 @@ func (h *Handlers) eventLogViews(
 		return nil, false
 	}
 
+	entrypoints, err := h.entrypointNames(webhookID)
+	if err != nil {
+		h.serverError(w, r, "failed to load entrypoints", err)
+
+		return nil, false
+	}
+
 	for i := range rows {
 		result[i].Deliveries = h.newDeliveryViews(
 			eventDeliveries[i], targetMap, attempts,
 		)
 		result[i].ResubmitCount = resubmits[rows[i].ID]
+
+		name, ok := entrypoints[rows[i].EntrypointID]
+		if !ok {
+			name = "deleted entrypoint"
+		}
+
+		result[i].Entrypoint = name
 	}
 
 	return result, true