feat(8.0)!: delete fork/branch/commit/history/versions — superseded by the Db API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Tests: superseded suites deleted; fork/commit blocks excised from shared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/index.ts

@@ -146,6 +146,7 @@ export type {
   TxUnrelateOperation,
   TransactOptions,
   TransactReceipt,
+  TxLogEntry,
   CompactHistoryOptions,
   CompactHistoryResult,
   ChangedIds
@@ -221,23 +222,6 @@ export { MemoryStorage, createStorage }
 // FileSystemStorage is exported separately to avoid browser build issues.
 export { FileSystemStorage } from './storage/adapters/fileSystemStorage.js'
 
-// Export COW (Copy-on-Write) infrastructure
-import { CommitLog } from './storage/cow/CommitLog.js'
-import { CommitObject, CommitBuilder } from './storage/cow/CommitObject.js'
-import { BlobStorage } from './storage/cow/BlobStorage.js'
-import { RefManager } from './storage/cow/RefManager.js'
-import { TreeObject } from './storage/cow/TreeObject.js'
-
-export {
-  // COW infrastructure
-  CommitLog,
-  CommitObject,
-  CommitBuilder,
-  BlobStorage,
-  RefManager,
-  TreeObject
-}
-
 // Export types
 import type {
   Vector,