fix: replace hardcoded test passwords with runtime-generated UUIDs

Generate random passwords in global-setup and share via temp file so
all Playwright workers use the same credentials. Screenshot scripts
use module-level crypto.randomUUID() since they run single-process.
Unit test auth passwords also use randomUUID().

Eliminates security scanner alerts for passwords committed to git.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/screenshots/constants.ts

@@ -8,11 +8,11 @@ export const MOBILE_VIEWPORT = { width: 390, height: 844 };
 export const ADMIN = {
 	email: 'admin@bretzel.app',
 	displayName: 'Bretzel Admin',
-	password: 'bretzel2026!'
+	password: crypto.randomUUID()
 };
 
 export const COLLABORATOR = {
 	email: 'salzig@bretzel.app',
 	displayName: 'Salzig Bretzel',
-	password: 'salzig2026!!'
+	password: crypto.randomUUID()
 };