feat(8.0)!: delete fork/branch/commit/history/versions — superseded by the Db API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Tests: superseded suites deleted; fork/commit blocks excised from shared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

tests/integration/db-mvcc.test.ts

@@ -952,4 +952,42 @@ describe('8.0 Db API — generational MVCC', () => {
     await spec1.release()
     await db.release()
   })
+
+  it('transactionLog() returns committed entries newest first, with meta and limit', async () => {
+    const brain = await openMemoryBrain()
+
+    // Nothing committed yet — the log is empty (single-op writes do not log).
+    await brain.add({ id: uid('txlog-solo'), type: NounType.Document, data: 'solo', vector: vec(99), subtype: 'note' })
+    expect(await brain.transactionLog()).toEqual([])
+
+    const first = await brain.transact(
+      [{ op: 'add', id: uid('txlog-a'), type: NounType.Document, data: 'a', vector: vec(100), metadata: {} }],
+      { meta: { author: 'job-1' } }
+    )
+    const second = await brain.transact(
+      [{ op: 'update', id: uid('txlog-a'), metadata: { v: 2 } }],
+      { meta: { author: 'job-2' } }
+    )
+    const third = await brain.transact([{ op: 'update', id: uid('txlog-a'), metadata: { v: 3 } }])
+
+    const entries = await brain.transactionLog()
+    expect(entries.map((entry) => entry.generation)).toEqual([
+      third.generation,
+      second.generation,
+      first.generation
+    ])
+    expect(entries[1].meta).toEqual({ author: 'job-2' })
+    expect(entries[2].meta).toEqual({ author: 'job-1' })
+    expect(entries[0].meta).toBeUndefined()
+    for (const entry of entries) {
+      expect(entry.timestamp).toBeGreaterThan(0)
+    }
+
+    const limited = await brain.transactionLog({ limit: 2 })
+    expect(limited.map((entry) => entry.generation)).toEqual([third.generation, second.generation])
+
+    await first.release()
+    await second.release()
+    await third.release()
+  })
 })