docs: add Brainiall TTS extension

[fasuizu-br]

Summary

• add the hosted Brainiall TTS Streamable HTTP server to the extension catalog
• prompt for the Authorization header instead of embedding credentials
• keep the entry unendorsed and link to the public server repository

Validation

• jq empty documentation/static/servers.json
• verified unique server IDs
• production health endpoint returned ok
• anonymous MCP initialize returned HTTP 200 with protocol 2025-06-18 and server brainiall-tts 2.14.7
• git diff --check

The catalog entry does not claim endorsement, installs, customers, or revenue.

[alexhancock]

🤖 Thanks so much for this contribution!

We're retiring goose's own MCP server registry in favor of the official, community-governed MCP registry and its server.json format. Effective immediately we're no longer accepting new server contributions (or edits) to our registry, so I'm closing this PR.

Full context here: #10830

We'd love to see your extension published to the official registry instead — that's now the path for discoverability across the ecosystem. Thanks again for your interest in goose! 🙏