Give each event its own page and show bodies the same everywhere (closes #369)

Each row of the recent events on the webhook page links to the
event's own page, /hook/{id}/events/{eventID}, and expands to show its
body; only the newest starts expanded. The event's page shows its
details, its whole body and every delivery with its attempts.

One renderer, newBodyView with templates/event_body.html, shows a body
in all three places: whole up to 32 KiB, cut there in the lists with a
link to the event's page, JSON pretty-printed, a body of more than 200
lines or 32 KiB in a scrolling box, and a body that is not text left
out beside its download link. A resubmitted copy links to its
original's page.

Model: opus-5-5

internal/database/model_event.go

@@ -34,8 +34,8 @@ type Event struct {
 	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.
+	// is stored, so that the recent events list, which reads only the
+	// start of each body, knows the whole body's size.
 	BodyBytes int64 `gorm:"not null" json:"bodyBytes"`
 
 	// ResubmittedFromID names the event this one was copied from by