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/page_title_test.go

@@ -57,7 +57,11 @@ func TestEveryPageRendersItsOwnTitle(t *testing.T) {
 		},
 		{
 			"source_logs.html",
-			map[string]any{dataKeyWebhook: webhook, "TotalEvents": int64(0)},
+			map[string]any{
+				dataKeyWebhook: webhook,
+				dataKeyEvents:  []handlers.EventLogView{},
+				"TotalEvents":  int64(0),
+			},
 			"Full Event Log - orders - Webhooker",
 		},
 		{