fix(api): support server-side sorting for newest, oldest, and Z-A pagination in link listing

[wulukewu]

Problem

KV.list() returns pages in alphabetical key order, but the dashboard's sorting for "newest", "oldest", and "Z-A" (za) was done client-side on already-loaded data only. This means:

1. Wrong page priority — for newest, oldest, and Z-A sorting, the first page always contains alphabetically early slugs (A-Z), not the actual sorted entries. Users must scroll through all pages before seeing the correct top links.
2. Cursor skips entries — KV.list() cursor represents an alphabetical position. Any link created/sorted that falls before the cursor is never returned in subsequent pages during pagination.

Solution

Add a sort query parameter to GET /api/link/list supporting slug_asc (default), slug_desc (Z-A), createdAt_desc (newest), and createdAt_asc (oldest).

• For slug_asc (A-Z), the server continues to use native KV.list() for optimal performance.
• For slug_desc, createdAt_desc, and createdAt_asc, the server:
  1. Lists all KV keys (loops through KV.list() pages of 1000)
  2. Fetches all links
  3. Sorts by the requested criteria
  4. Returns the requested page with a custom cursor:
     • {createdAt}::{slug} for creation date sorting
     • {slug} for Z-A (slug_desc) sorting

The client-side sort for newest/oldest is removed, and all custom sorting relies on the server-side pagination.

Changes

• server/utils/link-store.ts — add listLinksSorted() supporting custom sorting criteria
• server/api/link/list.get.ts — add sort query param and route to listLinksSorted() or listLinks()
• layers/dashboard/app/components/dashboard/links/Index.vue — pass sort, reset list on sort change