Fix cover used-before-declaration

Every todo page exports cover from its <script module> block while referencing the {#snippet cover()} declared further down the file. svelte-check flags this as two errors per page.

Confirmed Problem

• 84 × "Variable 'cover' is used before being assigned."
• 84 × "Block-scoped variable 'cover' used before its declaration."
• 168 errors total, across 84 todo pages.

Scope

This is the dominant share of the 179 svelte-check errors. The fix is a single structural change to the documented todo-page pattern, applied across every page. Coordinates with fix-ci-type-errors.