Fix SonarQube issues, store sessions in Redis, use direct analytics URLs

- ApiSandboxController: reduce scan() returns from 4 to 3 via ternary
- ApiDocController: add MIME_JSON constant, extract buildInsomniaRequest()
  and buildInsomniaBody() to reduce cognitive complexity
- Store sessions in Redis to fix SSO disconnect with 2 PHP replicas
  (round-robin load balancing caused session loss on filesystem storage)
- Configure session cookie: 24h lifetime, secure auto, samesite lax
- Replace Caddy analytics proxies (/stats/*, /assets/perf.js, /sperf)
  with direct URLs to tools-security.esy-web.dev and cloudflareinsights.com
- Update JS tests for new direct analytics URLs

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

.env

@@ -32,6 +32,10 @@ DATABASE_URL="postgresql://app:secret@database:5432/ecosplay?serverVersion=16&ch
 MESSENGER_TRANSPORT_DSN=redis://redis:6379/messages
 ###< symfony/messenger ###
 
+###> session ###
+SESSION_HANDLER_DSN=redis://redis:6379/sessions
+###< session ###
+
 ###> symfony/mailer ###
 MAILER_DSN=smtp://mailpit:1025
 ###< symfony/mailer ###