fix(web): inverted condition broke hiding shared calendars

The per-device hide branch was gated on owned!==false (my own calendars) instead
of owned===false (shared with me), so unchecking a shared calendar hit the
owner-only enabled PUT and 404'd. Swap to owned===false.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/js/version.js

@@ -1,2 +1,2 @@
 // Increment APP_VERSION with every code change
-export const APP_VERSION = 'v80';
+export const APP_VERSION = 'v81';