fix: Critical production issue - enable remote model downloads by default

- Fix embedding system to work out-of-the-box on fresh npm installs
- Add proper BRAINY_ALLOW_REMOTE_MODELS environment variable support
- Implement smart defaults: remote models enabled by default in production
- Add graceful fallback from local-only to remote download
- Maintain backward compatibility with existing configurations
- Add production readiness test suite for future releases
- Provide clear error messages with actionable guidance

BREAKING: None - this only improves default behavior
FIXES: #critical-production-failure-1.1.0

models/.brainy-models-bundled

@@ -1,5 +0,0 @@
-{
-  "model": "Xenova/all-MiniLM-L6-v2",
-  "bundledAt": "2025-08-08T23:44:45.657Z",
-  "version": "1.0.0"
-}