feat(sacred-valley): drag-to-reorder with server-persisted layout

Adds HTML5 drag-to-reorder for .sv-card elements in Sacred Valley. The
pure moveId helper is unit-tested. Drop calls PUT /api/dashboard/layout
to persist the new card_order; DOM reflects the new order immediately.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/api.js

@@ -63,6 +63,7 @@ function promptForToken() {
 export const api = {
   get:   (p)        => call('GET',    p),
   post:  (p, body)  => call('POST',   p, body ?? {}),
+  put:   (p, body)  => call('PUT',    p, body ?? {}),
   patch: (p, body)  => call('PATCH',  p, body ?? {}),
   del:   (p)        => call('DELETE', p),
   setToken: (v) => localStorage.setItem(TOKEN_KEY, v),