test(8.0): Tier-1 integration via deterministic embedder (suite runnable again)

The integration suite loaded the real WASM model for every test, so a full run
took ~hours and reliably aborted (vitest reporter timeout) — which is why it was
never gated and silently rotted. Brainy already separates the embedder from all
other logic, so running integration with a deterministic embedder keeps every
code path real (HNSW build+search, graph traversal, metadata filtering,
transactions, storage/sharding, VFS, aggregation, import) while making the suite
complete in ~2 min on ANY machine — no GPU, no 16 GB requirement.

- Add isDeterministicEmbedMode() — a single source of truth for the test-embedder
  switch (BRAINY_DETERMINISTIC_EMBEDDINGS, plus the legacy BRAINY_UNIT_TEST alias),
  used by EmbeddingManager (init/embed/embedBatch) and brainy's eager-init guard.
- setup-integration.ts opts into it: Tier 1 = functional end-to-end. Real-model
  semantic quality + the real embedding pipeline move to a Tier-2 suite.

Full integration now runs 482 passing / 583 in ~2 min (was un-completable). The
remaining failures are pre-existing test rot, fixed next. Unit 1414 green.

src/brainy.ts

@@ -116,6 +116,7 @@ import { resolveJsHnswConfig, DEFAULT_RECALL } from './utils/recallPreset.js'
 import * as fs from 'node:fs'
 import { Db, type DbHost, type HistoricalQueryHandle } from './db/db.js'
 import { GenerationStore } from './db/generationStore.js'
+import { isDeterministicEmbedMode } from './embeddings/deterministicEmbedMode.js'
 import { GenerationConflictError } from './db/errors.js'
 import { MemoryStorage } from './storage/adapters/memoryStorage.js'
 import type {
@@ -885,9 +886,7 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       //
       // `eagerEmbeddings: false` is the explicit override to force lazy init
       // (first-embed) even when this instance is the active embedder.
-      const isUnitTestMode =
-        process.env.BRAINY_UNIT_TEST === 'true' ||
-        (globalThis as { __BRAINY_UNIT_TEST__?: boolean }).__BRAINY_UNIT_TEST__ === true
+      const isUnitTestMode = isDeterministicEmbedMode()
       const eager = this.config.eagerEmbeddings ?? true
       if (
         eager &&