Support remote source dev access

[ymichael]

Summary

• add BB_DEV_REMOTE=true for source dev remote access
• bind the Vite dev app to all interfaces in remote mode
• make dev browser WebSockets target the page host on the server port instead of localhost
• document the remote dev flow

Validation

• pnpm exec turbo run test --filter=@bb/config
• pnpm exec turbo run typecheck --filter=@bb/config
• pnpm exec turbo run typecheck --filter=@bb/app
• pnpm exec turbo run test --filter=@bb/app
• pnpm exec turbo run typecheck --filter=@bb/server