fix: #752 guard purgeStaleCacheEntries against undefined storage on Node 26

[Copilot]

On Node 26, localStorage and sessionStorage are defined as globals but resolve to undefined unless --localstorage-file is passed. Because purgeStaleCacheEntries is called at module scope with no guard, importing coalesce-vue throws a TypeError before any test runs — breaking every Vitest+jsdom suite on Node 26 that transitively imports the package.

Changes

• src/coalesce-vue/src/api-client.ts — added an early-return guard to purgeStaleCacheEntries; degrades silently to "nothing to purge" when storage is undefined/null or not a valid Storage object:

function purgeStaleCacheEntries(storage: Storage | undefined | null) {
  if (!storage || typeof storage.length !== "number") return;
  // ...
}

• Fixes coalesce-vue: purgeStaleCacheEntries runs unguarded at import, crashing on Node 26 #752