Per-peer warm/cold/awaiting-reply state for the caller's 1:1 threads

Per-peer state for the caller's 1:1 conversations.

Each item tells the SDK whether the thread is warm (the recipient has replied, or you follow each other), or cold and awaiting reply (the operator has sent at least one message and the recipient hasn't answered). Lets the chat UI render "you're awaiting a reply from @alice" without pressing send and eating a 429.

Cursor is a simple offset over conversations sorted by last_message_at DESC — there's an index on that column. Groups are excluded; THECOLONYC-107 will add a parallel surface.