feat(8.0): full query surface at historical generations via ephemeral index materialization

Historical Db values (now()/asOf() pins that history has moved past) now
serve the COMPLETE query surface - vector/hybrid search, graph traversal,
cursor pagination, and aggregation - by materializing ephemeral in-memory
indexes over the exact at-generation record set. The historical-query
throw is gone; NotYetSupportedAtHistoricalGenerationError is deleted.

Materializer (Brainy.materializeAtGeneration):
- Copies the at-G record set (live bytes for ids untouched since the pin,
  immutable before-images otherwise) into a fresh MemoryStorage; a final
  reconciliation pass under the commit mutex makes the copy exact even
  when transactions commit mid-build.
- Opens a read-only Brainy over the copy: init rebuilds the metadata and
  graph-adjacency indexes from the records; the vector index is built by
  inserting every at-G vector (the at-G HNSW graph never existed on disk,
  so there is nothing to restore). Host embedder and aggregate definitions
  are shared - no second model load, aggregates backfill at-G values.
- Cost is the documented contract: O(n at G) time and memory, ONCE per Db
  (handle cached; freed by release(), with a FinalizationRegistry backstop
  that also closes leaked readers). A native VersionedIndexProvider serves
  the same reads from retained segments with no rebuild.

Db routing (src/db/db.ts): metadata-level find()/related() keep the free
record path; index-only dimensions (query/vector/near/connected/cursor/
aggregate/includeRelations/non-metadata modes) route to the cached
materialization; unsupported where-operators on the record path re-route
there too instead of erroring. Speculative with() overlays keep the one
honest boundary - SpeculativeOverlayError (overlay entities carry no
embeddings, so index reads over them would be silently incomplete);
metadata find()/get()/filter related() work on overlays.

UpdateParams.vector contract now honored: an explicit pre-computed vector
applies directly (with dimension validation) in update() and transact
update ops, re-indexing HNSW - previously it was silently ignored unless
data also changed.

GraphAdjacencyIndex: adjacency now derives from the two verb-id LSM trees
filtered through the live-verb tombstone set (entity->entity edge trees
deleted - they carried no verb ids, so removeVerb could never tombstone
them and traversal served stale neighbors forever). Neighbor reads batch-
load live verbs via the unified cache; addVerb seeds the cache.

Proofs (tests/integration/db-mvcc.test.ts, 24 green): historical vector
search finds old vector placement including since-deleted entities;
historical graph traversal walks the old wiring after a rewire; historical
aggregation computes at-G group values; asOf() pins get the same surface;
the materialization builds once per Db and release() closes the ephemeral
reader (it refuses reads afterwards); overlays throw the documented error.
ADR-001 updated to the no-throws historical model.

src/types/brainy.types.ts

@@ -4,7 +4,7 @@
  * Beautiful, consistent, type-safe interfaces for the future of neural databases
  */
 
-import { Vector } from '../coreTypes.js'
+import { StorageAdapter, Vector } from '../coreTypes.js'
 import { NounType, VerbType } from './graphTypes.js'
 
 // ============= Core Types =============
@@ -1092,14 +1092,21 @@ export interface BrainyStats {
  * Brainy configuration
  */
 export interface BrainyConfig {
-  // Storage configuration
-  storage?: {
-    type: 'auto' | 'memory' | 'filesystem' | 's3' | 'r2' | 'opfs' | 'gcs'
-    /** Root directory for filesystem storage. Passed through to storage factories
-     *  including plugin-provided factories (e.g. Cortex mmap). */
-    rootDirectory?: string
-    options?: any
-  }
+  /**
+   * Storage configuration: either a config object resolved through the
+   * storage factory, or a pre-constructed adapter instance (used directly —
+   * e.g. `storage: new MemoryStorage()`; Brainy's historical-query
+   * materializer hands a pre-populated instance through this path).
+   */
+  storage?:
+    | {
+        type: 'auto' | 'memory' | 'filesystem'
+        /** Root directory for filesystem storage. Passed through to storage factories
+         *  including plugin-provided factories (e.g. native mmap providers). */
+        rootDirectory?: string
+        options?: any
+      }
+    | StorageAdapter
 
   // Index configuration
   index?: {