fix: show message for spaces skipped when duplicating - #4210

Description

Duplicating several spaces in admin settings now tells the admin which spaces were skipped because they're not a member, instead of skipping them silently.

Related Issue

• Fixes Duplicating several spaces skips spaces the admin isn't a member of without a message #4189

How Has This Been Tested?

• test environment: unit tests (Vitest), browser tests (Playwright) against a local OpenCloud
• test case 1: unit: one and several non-member spaces in the selection show the matching message, member spaces are still duplicated
• test case 2: browser: mixed selections with one and two non-member spaces, member-only selection and single duplicate from the spaces overview (desktop, toast on Pixel 7)

Types of changes

• Bugfix
• Enhancement (a change that doesn't break existing code or deployments)
• Breaking change (a modification that affects current functionality)
• Technical debt (addressing code that needs refactoring or improvements)
• Tests (adding or improving tests)
• Documentation (updates or additions to documentation)
• Maintenance (like dependency updates or tooling adjustments)