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/handlers/event_body.go

@@ -24,9 +24,10 @@ import (
 const eventBodyQuery = "SELECT cast(body as blob) " +
 	"FROM events WHERE id = ? AND webhook_id = ? AND deleted_at IS NULL"
 
-// HandleEventBodyDownload serves one event's stored body in
-// full, which the event log page cannot: it caps each rendered
-// body at maxRenderedBodyBytes.
+// HandleEventBodyDownload serves one event's stored body byte
+// for byte, which the pages do not: they show it as escaped
+// text, cut at maxRenderedBodyBytes in the lists of events, and
+// leave a binary one out.
 //
 // The bytes are attacker-supplied — anyone who can reach the
 // public receiver chooses them — and this route hands them back