Fix pages.remote.js types

src/lib/pages.remote.js has five type errors stemming from the inferred page object type and a possibly-null sortOrder.

Confirmed Problem

• 27:23 — Property 'cover' does not exist on the inferred page type.
• 55:52 — 'meta.sortOrder' is possibly 'null'.
• 55:67 — Property 'default' does not exist on type 'object'.
• 67:14 — Left-hand side of arithmetic must be number/bigint.
• 67:24 — Right-hand side of arithmetic must be number/bigint.