Add comprehensive documentation explaining why vote write-forward endpoints were removed: - OAuth DPoP tokens are cryptographically bound to client's private key - Backend cannot create DPoP proofs (doesn't have the key) - Solution: Clients write directly to their PDS using com.atproto.repo.createRecord/deleteRecord - AppView indexes votes from Jetstream for aggregation Also documented future work needed for subscriptions and blocking. See: docs/PRD_BACKLOG.md#oauth-dpop-token-architecture