Event log: only the newest event expanded, and only the 50 most recent (closes #349)

The event log now loads the 50 newest events in its query and opens
only the newest on load, as the recent events on a webhook's page
already do. With 50 at most there is never a second page, so paging is
gone: the page links, the `page` query parameter, the page number that
Replay and Resubmit carried back to the log, and `pageOrFirst` with its
test. The count beside the heading reads "50 most recent of N events"
when there are more. The comments and README lines that named `page` as
the query parameter the service reads now name `next` and `notice`.

Model: opus-5-5

internal/handlers/handlers.go

@@ -30,10 +30,9 @@ import (
 const (
 	// maxBodyShift is the bit shift for 1 MB body limit.
 	maxBodyShift = 20
-	// recentEventLimit is the number of recent events to show.
+	// recentEventLimit is the number of most recent events that a
+	// webhook's page and its event log show.
 	recentEventLimit = 50
-	// paginationPerPage is the number of items per page.
-	paginationPerPage = 25
 
 	// tmplKeyError is the template data key for an error message.
 	tmplKeyError = "Error"