Show 50 recent events with size, processing time and status (closes #347)

The webhook page's list, now headed "50 Most Recent Events", shows the 50 newest events, limited in the query. Each row adds the time received (relative, UTC on hover), the body size, the processing time (slowest delivery, queued to final outcome, retries included, "in progress" while pending), and, when the webhook has exactly one HTTP target, that target's latest HTTP status, coloured by class.

Each event now records its body size in a new body_bytes column when it is stored, so the list never reads bodies; the list loads only the delivery and attempt columns it shows, and a failed load is an error, not an empty list.

An existing event database must be recreated: the column is added in place, with no migration.

Model: opus-5-5

internal/database/model_event.go

@@ -31,6 +31,11 @@ type Event struct {
 	Body        string `gorm:"type:text"   json:"body"`
 	ContentType string `json:"contentType"`
 
+	// BodyBytes is the size of Body in bytes, recorded when the event
+	// is stored so the recent events list can show it without reading
+	// the body.
+	BodyBytes int64 `gorm:"not null" json:"bodyBytes"`
+
 	// ResubmittedFromID names the event this one was copied from by
 	// an operator resubmit. It is nil for an event that arrived on
 	// the receiver, which is every event created before the column