Fix empty Caddy and pg_stat_statements panels in service-health dashboard

- Caddy Response Status Codes: caddy_http_responses_total doesn't exist,
  use caddy_http_response_duration_seconds_count which has the code label
- pg_stat_statements: enable extension in init script, add custom queries
  config for postgres-exporter, remove invalid datname filter from query
- Add postgres/queries.yml to cd-infra SCP sources

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infrastructure/postgres/init-grafana-user.sql

@@ -1,3 +1,6 @@
+-- Enable pg_stat_statements for query performance monitoring
+CREATE EXTENSION IF NOT EXISTS pg_stat_statements;
+
 -- Read-only user for Grafana dashboards
 -- Password is set via: ALTER ROLE grafana_reader PASSWORD '<from SOPS>'
 -- Run by cd-infra deploy script after container start