feat(8.0)!: delete fork/branch/commit/history/versions — superseded by the Db API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Tests: superseded suites deleted; fork/commit blocks excised from shared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

@@ -52,30 +52,10 @@ export interface StorageOptions {
     [key: string]: any
   }
 
-  /** Branch name for COW storage (filesystem only). */
-  branch?: string
-
-  /** Whether to enable COW blob compression. Default `true`. */
-  enableCompression?: boolean
-
   /** Operation tuning (timeouts, retry budgets) passed through to the adapter. */
   operationConfig?: OperationConfig
 }
 
-/**
- * Attach the COW (copy-on-write) options to the adapter so the storage's
- * branch + compression settings are honored when the adapter's
- * `initializeCOW()` hook fires later in `brain.init()`.
- */
-function configureCOW(storage: any, options?: StorageOptions): void {
-  if (typeof storage?.initializeCOW === 'function') {
-    storage._cowOptions = {
-      branch: options?.branch || 'main',
-      enableCompression: options?.enableCompression !== false
-    }
-  }
-}
-
 /**
  * Resolve `StorageOptions` to a concrete storage adapter.
  *
@@ -85,9 +65,7 @@ function configureCOW(storage: any, options?: StorageOptions): void {
  * - `forceFileSystemStorage: true` returns `FileSystemStorage`.
  */
 export async function createStorage(options: StorageOptions = {}): Promise<StorageAdapter> {
-  const storage = await pickAdapter(options)
-  configureCOW(storage, options)
-  return storage
+  return pickAdapter(options)
 }
 
 async function pickAdapter(options: StorageOptions): Promise<StorageAdapter> {