Read the public intelligence change feed

Returns immutable public-resource lifecycle events in global order. An authenticated API key receives globally visible intelligence changes plus changes owned by its user or workspace tenant. Anonymous x402 requests receive globally visible intelligence changes only; tenant records are never exposed across scopes. The `watermark` is an opaque exclusive checkpoint: persist the returned value and send it on the next request. Replaying a checkpoint never skips later events and may safely be retried after a consumer failure. Deleted resources are represented as tombstones. Events are append-only in schema version `1.0`; no retention expiry is currently applied.