Mention Brix and follow replies in order

Brix mentions complete more reliably while you write a comment, and nested replies stay in chronological order when opened from a notification.

What’s changed

• Type @brix followed by a space to complete the mention without creating a broken founder-profile link.
• Clear the waiting status when Brix’s answer arrives. Brix replies retain their existing Growth and Scale access requirements.
• Read replies from oldest to newest, with a notification’s target reply kept in its chronological position.