Release v4.7.15-beta.1

What's Changed

• chore(deps): 升级 mongo-driver 与 modernc libc/memory 间接依赖 (28602d23)
• feat(proxy): multimodal fallback routing for models without vision (9c07777a)
• feat(web): multimodal fallback settings UI (ff7a3bc6)
• fix(settings): hot-reload multimodal fallback configuration (667208a2)
• feat(logs): record upstream response model (682abf8c)

Full Changelog: v4.7.14-beta.3...v4.7.15-beta.1