Switch logs paging to keyset pagination

[trieloff]

Problem
Logs pagination uses OFFSET, which becomes slower as offsets grow and can skip/duplicate rows as new data arrives.

Proposed change

• Replace OFFSET pagination with keyset pagination using timestamp (and a tie-breaker if needed).
• Persist the last-seen cursor and request the next page using WHERE timestamp < :cursor.

Acceptance criteria

• Large paginations remain performant.
• No duplicates or gaps when new data arrives during paging.

[trieloff]

Analyze if we can use Cursor-based pagination and if there is an opportunity to combine the cursor hashes for pagination with the hashes we use for sampling in #89