Fix Meta.svelte types

src/lib/Meta.svelte passes a {} fallback value into props typed as string or number.

Confirmed Problem

• 42:41 — Type '{}' is not assignable to type 'string'.
• 79:32 — Argument of type '{}' is not assignable to parameter of type 'string'.
• 84:25 — Argument of type '{}' is not assignable to parameter of type 'number'.