CVE-2026-45667: Open WebUI: Unauthenticated endpoint can trigger embedding generation (cost/DoS)

GET /api/v1/memories/ef is accessible without authentication and executes request.app.state.EMBEDDING_FUNCTION(...). This allows any unauthenticated caller to trigger embedding generation which can lead to direct cost exposure if a paid provider is used. Code reference: backend/open_webui/routers/memories.py (@router.get("/ef") -> calls request.app.state.EMBEDDING_FUNCTION("hello world")).