GET /v2/social/activity/ws

Upgrades to the authenticated provider-neutral Social Activity feed. Offer arbital.terminal.v1 and the ticket_protocol returned by POST /v2/social/activity/ws/tickets as WebSocket subprotocols. Every thesis-containing column is server-normalized to asset_scope=trending, including legacy columns that omit it and combined trade-plus-thesis columns. Every snapshot is a total replacement rebuilt from current committed activity and Trending theses, with reserved capacity for both. When external theses and application trades use independent sources, the server sends total replacement snapshots; item sequences belong to their source and the snapshot watermark is a summary, not a cross-source replay cursor. Clients replace the snapshot atomically and must not discard items by comparing sequences across sources.