Proposal: add-explore-merged-timeline

The Explore canvas needs a single durable server endpoint that can serve a fully-paginated, time-ordered feed spanning ALL of the owner's sources. The previous approach (per-stream fan-out capped at a fixed total, assembled in the browser layer) has three compounding defects:

The reference implementation SHALL expose GET /ref/explore/records as a durable, owner-session-authenticated reference route that returns a page of time-ordered records merged across all of the owner's (connectorinstance_id, stream) partitions. This route is a reference/operator surface, NOT a PDPP Core protocol route, and SHALL NOT be reachable over /mcp or with a grant-scoped token. Its response shape is designed exclusively for the console Explore canvas and clients MUST NOT depend on it as a stable external protocol.