New-thread send shortcut: review evidence

Review evidence for the new-thread send-shortcut fix. This prerelease contains screenshots and recordings only, not application binaries.

Before: upstream main at 67c0fc0. After: 47e1a88.

Captured with T3 Code Browser on Linux Chromium against an isolated development instance and disposable project. Native Ctrl+Enter events exercise the Linux Mod shortcut; macOS uses Command. Before, Ctrl+Enter starts new chats in the background under both modifier-required send settings. After, it opens the new chat, while Ctrl+Shift+Enter still starts in background. Screenshots and recordings are unmodified.