feat: ID-first storage architecture + remove memory-unsafe APIs (v6.0.0)

BREAKING CHANGES:

**ID-First Storage Paths**
- Direct O(1) entity access without type lookups
- Before: entities/nouns/{TYPE}/metadata/{SHARD}/{ID}.json
- After:  entities/nouns/{SHARD}/{ID}/metadata.json
- Migration handled automatically on first init()

**Removed Memory-Unsafe APIs**
- Removed brain.merge() - loaded all entities into memory
- Removed brain.diff() - loaded all entities into memory
- Removed brain.data().backup() - loaded all entities into memory
- Removed brain.data().restore() - depended on backup()
- Removed CLI commands: backup, restore, cow merge

**Migration Paths**
- merge() → Use checkout() or manually copy entities with pagination
- diff() → Use asOf() with manual paginated comparison
- backup() → Use fork() for instant COW snapshots
- restore() → Use checkout() to switch to snapshot branch

Core Improvements:
- ✅ All 8 storage adapters properly call super.init()
- ✅ GraphAdjacencyIndex integration in BaseStorage.init()
- ✅ Fixed ID-first path bugs (vector.json → vectors.json)
- ✅ Fixed MemoryStorage.initializeCounts() for ID-first paths
- ✅ New VFS APIs: du(), access(), find()
- ✅ Comprehensive documentation with migration guides

Storage Adapters Fixed:
- MemoryStorage, FileSystemStorage, AzureBlobStorage
- GCSStorage, R2Storage, S3CompatibleStorage
- OPFSStorage, HistoricalStorageAdapter

Files Changed: 28 files, +1,075/-1,933 lines (net -858)

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

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

docs/transactions.md

@@ -123,25 +123,25 @@ await brain.relate({ from: id1, to: id2, type: VerbType.RelatesTo })
 - Transaction operations don't need to know about shards
 - Rollback works across all shards involved
 
-### TypeAware Storage
+### ID-First Storage (v6.0.0+)
 
 ✅ **Fully Compatible**
 
-Transactions work with type-specific routing:
+Transactions work with direct ID-first paths - no type routing needed!
 
 ```typescript
-// Entities routed to type-specific storage paths
+// Entities stored with direct ID-first paths
 const personId = await brain.add({
   data: { name: 'John Doe' },
-  type: NounType.Person  // → entities/nouns/person/<shard>/...
+  type: NounType.Person  // → entities/nouns/{shard}/{id}/metadata.json
 })
 
 const orgId = await brain.add({
   data: { name: 'Acme Corp' },
-  type: NounType.Organization  // → entities/nouns/organization/<shard>/...
+  type: NounType.Organization  // → entities/nouns/{shard}/{id}/metadata.json
 })
 
-// Type changes handled atomically
+// Type changes handled atomically (type is just metadata)
 await brain.update({
   id: personId,
   type: NounType.Organization,  // Type change
@@ -150,10 +150,11 @@ await brain.update({
 ```
 
 **How It Works:**
-- Type information carried in metadata
-- Storage layer handles type-specific routing
-- Type cache updated/restored during rollback
+- Type information stored in metadata.noun field
+- Storage layer uses O(1) ID-first path construction
+- No type cache needed (removed in v6.0.0)
 - Type counters adjusted on commit/rollback
+- 40x faster on cloud storage (eliminates 42-type search)
 
 ### Distributed Storage