feat: brain.find() excludes VFS by default (Option 3C)

Added includeVFS parameter to FindParams:
- brain.find() excludes VFS entities by default (clean knowledge graph)
- Opt-in with brain.find({ includeVFS: true })
- Automatically excludes VFS in all query paths (empty, metadata, vector)
- Respects explicit where: { isVFS: ... } queries

Implementation:
- Empty query path: Apply VFS filtering even with no criteria
- Metadata query path: Filter out isVFS: true by default
- Vector search path: Apply VFS filter after search
- Skip auto-exclusion if where clause explicitly queries isVFS

Architecture (Option 3C):
- VFS entities are first-class graph entities
- Marked with isVFS: true flag
- Separated via filtering, not storage
- Enables VFS-knowledge relationships

Moved internal docs to .strategy/:
- README_STORAGE_EXPLORATION.md
- EXPLORATION_SUMMARY.md
- STORAGE_FILES_REFERENCE.md
- STORAGE_ADAPTER_QUICK_REFERENCE.md
- SECURITY.md

src/types/brainy.types.ts

@@ -185,6 +185,7 @@ export interface FindParams<T = any> {
   mode?: SearchMode          // Search strategy
   explain?: boolean          // Return scoring explanation
   includeRelations?: boolean // Include entity relationships
+  includeVFS?: boolean       // v4.3.3: Include VFS entities (default: false for knowledge queries)
   service?: string           // Multi-tenancy filter
   
   // Triple Intelligence Fusion