feat: comprehensive metadata namespace architecture and cleanup system

BREAKING CHANGE: Remove hard delete option from deleteVerb() for consistent API

- Add complete metadata namespace architecture with O(1) soft delete performance
- Implement periodic cleanup system for old soft-deleted items
- Add restore methods for both nouns and verbs
- Require metadata contracts for all augmentations
- Eliminate namespace collisions with clean separation (_brainy, _augmentations, _audit)
- Optimize index performance using flattened dot-notation for O(1) lookups
- Add comprehensive augmentation safety system with type-safe access control
- Maintain full backward compatibility for existing data
- Add enterprise-grade cleanup with configurable age thresholds and batch processing

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/augmentations/cacheAugmentation.ts

@@ -31,6 +31,7 @@ export interface CacheConfig {
 export class CacheAugmentation extends BaseAugmentation {
   readonly name = 'cache'
   readonly timing = 'around' as const
+  readonly metadata = 'none' as const  // Cache doesn't access metadata
   operations = ['search', 'add', 'delete', 'clear', 'all'] as ('search' | 'add' | 'delete' | 'clear' | 'all')[]
   readonly priority = 50 // Mid-priority, runs after data operations