Flyto2 Core: Unauthenticated flyto-verification /run: callback_url SSRF and internal runner-secret exfiltration

Flyto2 Core is an execution kernel for automation and AI-agent workflows. Prior to 2.26.7, the standalone flyto-verification service in src/core/verification_service.py exposes unauthenticated POST /run on 0.0.0.0:8344 and uses client-supplied callback_url for an outbound POST with X-Internal-Key: $FLYTO_RUNNER_SECRET while bypassing target_allowed, allowing unauthenticated SSRF and runner secret exfiltration. This issue is fixed in version 2.26.7.