cross-cutting: typed escape hatch — client.raw for direct SDK access

[productdevbook]

Wrappers become permanent subsets of provider APIs. Users need an escape hatch that's still typed.

Evidence

• `想问下这个插件里边没有 login 的方法吗，我看官方是有的 tawk/tawk-messenger-react#42` — "no login method" 想问下这个插件里边没有 login 的方法吗，我看官方是有的 tawk/tawk-messenger-react#42
• `Out of date tawk/tawk-messenger-react#23` — "Out of date" Out of date tawk/tawk-messenger-react#23
• Pattern repeats across every wrapper over multi-year timelines

Tasks

• `client.raw` — typed reference to the underlying global (Intercom, `$crisp`, `Tawk_API`, `zE`, `HubSpotConversations`, `$chatwoot`, `drift`, `fcWidget`, `LiveChatWidget`, `olark`, `messenger`, `Beacon`, `smartsupp`, `LiveAgent`, `gist`, `jivo_api`, `tidioChatApi`)
• Typed via ambient globals
• Returns `undefined` before boot — users must `await client.ready`

[productdevbook]

Implemented in this commit