3cd2a678a6
Codemod-driven migration of 55 .svelte files from the deprecated $app/stores module to the rune-based $app/state ($page.x → page.x, no auto-subscription wrapper). Two custom writable() stores converted to .svelte.ts factory functions matching the existing theme store pattern, with consumers updated to use .value getters and the explicit .set() method. UserHeader.svelte's login link now guards page.url.search behind the browser flag — search-param access throws during prerender, and this defensive change unblocks future prerender adoption on any page that includes the header.