feat: v0.49 - Filter discovery API, remove deprecated methods, improve performance

BREAKING CHANGES:
- Removed deprecated getAllNouns() and getAllVerbs() methods
- All internal usage migrated to pagination-based methods

New Features:
- Filter Discovery API:
  - getFilterValues(field): Get all available values for a field
  - getFilterFields(): Get all filterable fields
  - Enables dynamic filter UI generation with O(1) field discovery
- Hybrid metadata indexing with field-level indexes
- Adaptive auto-flush for optimal performance
- LRU caching for metadata indexes

Improvements:
- Fixed ENAMETOOLONG errors from vector-based filenames
- Safe filename generation using hash-based approach
- Scalable chunked value storage for millions of entries
- Performance optimization with adaptive flush thresholds
- Added support for $includes operator in metadata filters

Technical:
- Replaced vector-based filenames with safe hash approach
- Implemented MetadataIndexCache with existing SearchCache pattern
- Field indexes enable O(1) filter discovery
- Adaptive flush based on performance metrics (20-200 entries)
- All tests passing with improved metadata filtering

README.md

@@ -11,7 +11,26 @@
 
 </div>
 
-## 🔥 MAJOR UPDATES: What's New in v0.46+ & v0.48+
+## 🔥 MAJOR UPDATES: What's New in v0.49, v0.48 & v0.46+
+
+### 🎯 **v0.49: Filter Discovery & Performance Improvements**
+
+**Discover available filters and scale to millions of items!**
+
+```javascript
+// Discover what filters are available
+const categories = await brainy.getFilterValues('category')
+// Returns: ['electronics', 'books', 'clothing', ...]
+
+const fields = await brainy.getFilterFields()
+// Returns: ['category', 'price', 'brand', 'rating', ...]
+```
+
+- ✅ **Filter Discovery API**: See what values are available for filtering
+- ✅ **Improved Performance**: Removed deprecated methods, now uses pagination everywhere
+- ✅ **Better Scalability**: Hybrid indexing approach handles millions of items
+- ✅ **Smart Caching**: LRU cache for frequently accessed filters
+- ✅ **Zero Configuration**: Everything auto-optimizes based on usage patterns
 
 ### 🚀 **v0.48: MongoDB-Style Metadata Filtering**