fix: dedupe alert_rules before creating unique index in setup_indexes()

The unique index on alert_rules.name was being created before duplicates
were cleaned up, causing DuplicateKeyError on startup when existing
duplicates were present. Move deduplication into setup_indexes() so it
runs before the unique index is created.

v1.7.6

backend/database.py

@@ -12,6 +12,20 @@ alerts_collection = db["alerts"]
 logger = structlog.get_logger("aoc.database")
 
 
+def _dedupe_alert_rules():
+    """Remove duplicate alert_rules by name, keeping the oldest document."""
+    try:
+        pipeline = [
+            {"$sort": {"_id": ASCENDING}},
+            {"$group": {"_id": "$name", "first_id": {"$first": "$_id"}}},
+        ]
+        seen = {doc["_id"]: doc["first_id"] for doc in db["alert_rules"].aggregate(pipeline)}
+        for name, keep_id in seen.items():
+            db["alert_rules"].delete_many({"name": name, "_id": {"$ne": keep_id}})
+    except Exception:
+        pass  # Collection may not exist yet
+
+
 def setup_indexes(max_retries: int = 5, delay: float = 2.0):
     """Ensure MongoDB indexes exist. Retries on connection errors."""
     from time import sleep
@@ -23,6 +37,7 @@ def setup_indexes(max_retries: int = 5, delay: float = 2.0):
             events_collection.create_index([("service", ASCENDING), ("timestamp", DESCENDING)])
             events_collection.create_index("id")
             saved_searches_collection.create_index([("created_by", ASCENDING), ("created_at", DESCENDING)])
+            _dedupe_alert_rules()
             db["alert_rules"].create_index("name", unique=True)
             events_collection.create_index(
                 [("actor_display", TEXT), ("raw_text", TEXT), ("operation", TEXT)],