refactor web pagination and add partitioned events, flap/timeout showcase agents

deploy/showcase/checks/flap.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+# Alternates between ok and critical every ~30 seconds to demonstrate flapping.
+slot=$(( $(date +%s) / 30 % 2 ))
+if [ "$slot" -eq 0 ]; then
+  echo "critical: flap window down"
+  exit 2
+fi
+echo "ok: flap window up"
+exit 0

deploy/showcase/checks/sleep_long.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+# Sleeps longer than the configured timeout to demonstrate timeout handling.
+sleep 30
+echo "should never reach here"
+exit 0