fix(wb-alerts): surface Phase-0 telemetry counters in /health

The /health handler builds its "monitor" payload from an explicit field
list, so the new _stats counters added in 3b20b4c (security_discarded_today,
cp_messages_seen_today, cp_whitelist_miss_today) were never exposed even
though get_stats() returns them. Map the three into the response.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

services/westbank-alerts/app/main.py

@@ -483,6 +483,10 @@ async def health():
             "messages_today":   monitor_stats.get("messages_today", 0),
             "alerts_today":     monitor_stats.get("alerts_today", 0),
             "cp_updates_today": monitor_stats.get("cp_updates_today", 0),
+            # Phase-0 telemetry: the otherwise-invisible drops.
+            "security_discarded_today": monitor_stats.get("security_discarded_today", 0),
+            "cp_messages_seen_today":   monitor_stats.get("cp_messages_seen_today", 0),
+            "cp_whitelist_miss_today":  monitor_stats.get("cp_whitelist_miss_today", 0),
         },
         "checkpoints": {
             "last_update": cp_last,