Shared resource blocking and booking flow fixes

What changed

Spaces can now share a physical resource so booking availability checks block overlapping reservations across related setups, not just within one individual space record.

Public booking checkout now keeps add-ons in the intended order, and tenant settings keep Supported Niches selections when you save them.

Why this matters

• One booked setup can reserve the entire room when spaces represent shared physical equipment or layouts.
• Checkout is easier to scan because add-ons appear in the order the studio configured.
• Settings no longer appear to lose a niche selection after refresh.
• A few admin client flows are less likely to throw a client-side application error during common tasks.