Cataclysm-DDA experimental build 2026-08-27-0619

What's Changed

• [Xedra Evolved] Add achievement for beating the Undying Vengeance challenge by @Standing-Storm in #88432
• [Xedra Evolved] Crossing the threshold as a changeling gives you a worse Iron Allergy by @Standing-Storm in #88428
• Add HIDDEN_SPELL flag to some mod spells by @Standing-Storm in #88427

Full Changelog: cdda-experimental-2026-08-27-0524...cdda-experimental-2026-08-27-0619