feat(8.0)!: delete fork/branch/commit/history/versions — superseded by the Db API

The COW version-control surface (fork, branches, checkout, commit,
getHistory/streamHistory, asOfCommit, brain.versions) is gone, along with
its subsystems: src/versioning/, the COW object store (CommitLog,
CommitObject, RefManager, TreeObject), HistoricalStorageAdapter, and the
TypeAwareHNSWIndex path it kept alive. The Db API (now/transact/asOf/
with/persist/restore) is the one versioning model in 8.0.

Survivors and replacements:
- BlobStorage survives (the VFS stores file content through it), relocated
  to src/storage/blobStorage.ts with binaryDataCodec.ts; its adapter
  interface is now BlobStoreAdapter, slimmed to the consumed surface
  (write/read/has/delete/getMetadata + MIME-aware compression policy).
- brain.migrate() backup branches are replaced by persist-before-migrate:
  MigrateOptions.backupTo persists a hard-link snapshot of the current
  generation before any transform runs; MigrationResult.backupPath reports
  it, and brain.restore(path) brings it back wholesale.
- CLI: cow.ts (fork/branch/checkout/history/migrate) is replaced by
  snapshot.ts — snapshot <path>, restore <path>, history (tx-log),
  generation.
- New public read API: brain.transactionLog({limit}) exposes the reified
  tx-log (generation/timestamp/meta, newest first) that backs the CLI
  history command; TxLogEntry is exported.

Tests: superseded suites deleted; fork/commit blocks excised from shared
suites; BlobStorage tests relocated + reworked against the slimmed store;
migration tests now prove the backupTo snapshot/restore round trip; new
transactionLog coverage in db-mvcc.

src/transaction/operations/IndexOperations.ts

@@ -20,8 +20,7 @@ import type { Operation, RollbackAction } from '../types.js'
  *
  * Rollback strategy:
  * - Remove item from index
- *
- * Note: Works with both JsHnswVectorIndex and TypeAwareHNSWIndex
+
  */
 export class AddToHNSWOperation implements Operation {
   readonly name = 'AddToHNSW'

src/transaction/operations/StorageOperations.ts

@@ -5,10 +5,9 @@
  * Each operation can be executed and rolled back atomically.
  *
  * Supports:
- * - All 8 storage adapters (FileSystem, S3, Memory, OPFS, GCS, Azure, R2, TypeAware)
+ * - Both storage adapters (FileSystem, Memory)
  * - Nouns (entities) and Verbs (relationships)
  * - Metadata and vector data
- * - COW (Copy-on-Write) storage
  */
 
 import type { StorageAdapter, HNSWNoun, HNSWVerb, NounMetadata, VerbMetadata } from '../../coreTypes.js'