Add compound DB indexes for hot query paths

network_events: idx_event_lookup (event_type, target_name, target_detail, resolved_at)
  - Covers the upsert_event SELECT which runs every cycle per monitored entity
  - Replaces three separate single-column index scans with one covering lookup

suppression_rules: idx_sup_lookup (active, target_type, target_name, target_detail)
  - Covers is_suppressed() queries (now redundant for runtime due to in-memory
    check_suppressed, but ensures fast get_active_suppressions() loading per cycle)

Both indexes created on live DB (MariaDB LXC 149).

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

schema.sql

@@ -24,7 +24,9 @@ CREATE TABLE IF NOT EXISTS network_events (
 
   INDEX idx_active       (resolved_at),
   INDEX idx_target       (target_name, target_detail),
-  INDEX idx_type     (event_type)
+  INDEX idx_type         (event_type),
+  -- Compound index for hot upsert_event lookup: event_type+target+resolved_at
+  INDEX idx_event_lookup (event_type, target_name, target_detail, resolved_at)
 ) ENGINE=InnoDB;
 
 -- ── Suppression rules ─────────────────────────────────────────────────
@@ -39,7 +41,9 @@ CREATE TABLE IF NOT EXISTS suppression_rules (
   expires_at    TIMESTAMP    NULL,       -- NULL = manual (never auto-expires)
   active        BOOLEAN      NOT NULL DEFAULT TRUE,
 
-  INDEX idx_active_exp (active, expires_at)
+  INDEX idx_active_exp  (active, expires_at),
+  -- For suppression lookup by type+name
+  INDEX idx_sup_lookup  (active, target_type, target_name, target_detail)
 ) ENGINE=InnoDB;
 
 -- ── Monitor state (key/value store for snapshot + baseline) ───────────