feat(8.0)!: delete fork/branch/commit/history/versions — superseded by the Db API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Tests: superseded suites deleted; fork/commit blocks excised from shared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

@@ -0,0 +1,80 @@
+/**
+ * Hybrid Search VFS Integration Tests
+ *
+ * Verifies that hybrid search works correctly with VFS entities:
+ * file content is searchable by default, and `excludeVFS` filters
+ * VFS entities out of results.
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { Brainy } from '../../src/brainy'
+import { NounType } from '../../src/types/graphTypes'
+import * as fs from 'fs'
+import * as path from 'path'
+import * as os from 'os'
+
+describe('Hybrid Search with VFS', () => {
+  let brain: Brainy<any>
+  let testDir: string
+
+  beforeEach(async () => {
+    testDir = path.join(os.tmpdir(), `brainy-hybrid-vfs-test-${Date.now()}`)
+    fs.mkdirSync(testDir, { recursive: true })
+
+    brain = new Brainy({ requireSubtype: false,
+      storage: {
+        type: 'filesystem',
+        options: { basePath: testDir }
+      }
+    })
+    await brain.init()
+  })
+
+  afterEach(async () => {
+    await brain.close()
+    // Cleanup test directory
+    try {
+      fs.rmSync(testDir, { recursive: true, force: true })
+    } catch (e) {
+      // Ignore cleanup errors
+    }
+  })
+
+  it('should include VFS file content in hybrid search', async () => {
+    // Write a file via VFS
+    const vfs = brain.vfs
+    await vfs.writeFile('/docs/readme.txt', 'This is a readme file with important information')
+
+    // Search should find VFS content
+    const results = await brain.find({
+      query: 'readme important',
+      limit: 10
+    })
+
+    // VFS entities should appear in results
+    expect(results.length).toBeGreaterThan(0)
+  })
+
+  it('should exclude VFS with excludeVFS flag in hybrid search', async () => {
+    // Add regular entity
+    const entityId = await brain.add({
+      data: 'regular document about readme files',
+      type: NounType.Document,
+      metadata: { source: 'api' }
+    })
+
+    // Write VFS file
+    await brain.vfs.writeFile('/readme.md', 'VFS readme content')
+
+    // Search with excludeVFS should only find regular entity
+    const results = await brain.find({
+      query: 'readme',
+      excludeVFS: true,
+      limit: 10
+    })
+
+    expect(results.some(r => r.id === entityId)).toBe(true)
+    // VFS entities should be excluded
+    expect(results.every(r => !r.metadata?.vfsType)).toBe(true)
+  })
+})