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/server/routes_test.go

@@ -364,6 +364,7 @@ func (e *testEnv) seedEvent(
 		WebhookID:   webhookID,
 		Method:      http.MethodPost,
 		Body:        body,
+		BodyBytes:   int64(len(body)),
 		ContentType: "application/octet-stream",
 	}
 
@@ -1247,6 +1248,48 @@ func TestHook_LinksBetweenPages(t *testing.T) {
 	}
 }
 
+// TestEventPage_OpenedFromRecentEvents follows the Open link of a
+// row in the recent events on the webhook page through the
+// production router to the event's own page, which shows the body
+// and links back. Another user gets a 404 at the same URL, and a
+// logged-out request is sent to log in.
+func TestEventPage_OpenedFromRecentEvents(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnv(t)
+
+	ownerID, _ := env.seedUser(t, "owner", "somepassword")
+	cookies := env.authCookies(t, ownerID, "owner")
+	wh := env.seedWebhook(t, ownerID)
+	evt := env.seedEvent(t, wh.ID, "OWNERS-PAYLOAD-3e9d")
+
+	page := "/hook/" + wh.ID
+	path := env.urlFrom(t, page, `href="([^"]+)"[^>]*>Open<`, cookies)
+
+	require.Equal(t, page+"/events/"+evt.ID, path)
+
+	w := env.get(path, cookies)
+	require.Equal(t, http.StatusOK, w.Code)
+	assert.Contains(t, w.Body.String(), "OWNERS-PAYLOAD-3e9d")
+	assert.Equal(
+		t, page,
+		env.urlFrom(t, path, `href="([^"]+)"[^>]*>&larr; Back to `, cookies),
+	)
+
+	intruderID, _ := env.seedUser(t, "intruder", "somepassword")
+
+	w = env.get(path, env.authCookies(t, intruderID, "intruder"))
+	assert.Equal(t, http.StatusNotFound, w.Code)
+	assert.NotContains(t, w.Body.String(), "OWNERS-PAYLOAD-3e9d")
+
+	anon := env.get(path, nil)
+	assert.Equal(t, http.StatusSeeOther, anon.Code)
+	assert.Equal(
+		t, "/pages/login?next="+url.QueryEscape(path),
+		anon.Header().Get("Location"),
+	)
+}
+
 // TestSourceLogs_TruncationLinkDownloadsTheBody walks the whole
 // feature the way a user does: render the event log page through
 // the production router, take the download URL out of the markup