Add pagination to event queries, input validation, daily event purge

- get_active_events() now takes limit/offset (default 200) to cap unbounded queries
- count_active_events() added to return total for pagination display
- /api/events supports ?limit=, ?offset=, ?status= query params (max 1000)
- /api/status includes total_active count alongside paginated events list
- index() route passes total_active to template for server-side truncation notice
- Show "Showing X of Y" notice in dashboard when events are truncated
- Suppression POST validates: reason ≤500 chars, target_name/detail ≤255 chars
- _purge_old_jobs_loop runs purge_old_resolved_events(90d) once per day

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

templates/index.html

@@ -277,6 +277,9 @@
   </div>
   <div id="events-table-wrap">
     {% if events %}
+    {% if total_active is defined and total_active > events|length %}
+    <div class="pagination-notice">Showing {{ events|length }} of {{ total_active }} active alerts &mdash; <a href="/api/events?limit=1000">view all via API</a></div>
+    {% endif %}
     <div class="table-wrap">
       <table class="data-table" id="events-table">
         <thead>