feat(8.0): API simplification — remove neural()/Db.search, one storage path key, integration→0

8.0 RC cleanup toward "one place per thing, zero-config, no deprecation":

- Remove the `brain.neural()` clustering namespace (ImprovedNeuralAPI + the dead
  legacy NeuralAPI + the neural CLI + neural-only types). Similarity is `find({vector})`
  / `similar({to})`; attribute grouping is the aggregation `GROUP BY` engine. The separate
  entity-extraction / smart-import feature (NeuralImport, NeuralEntityExtractor, SmartExtractor,
  NaturalLanguageProcessor, `brain.extract()`/`brain.nlp()`) is kept.
- Remove `Db.search()`; `find()` is the one query verb (accepts a bare string or FindParams).
  Fix the bundled MCP client, which called a non-existent `brain.search(query, limit)` →
  now `find({ query, limit })`.
- Storage config: collapse to one canonical top-level `path` key. The pre-8.0 aliases
  (`rootDirectory`, `options.*`, `fileSystemStorage.*`) are removed and now THROW with the
  exact rename instead of silently defaulting to `./brainy-data` on upgrade. A single resolver
  feeds createStorage, the 7.x→8.0 migration probe, and the plugin-factory handoff, so a native
  storage provider resolves the identical root (no split-brain).
- Fix `similar({ threshold })`: the min-similarity filter was silently dropped; it is now
  applied as a post-filter on `result.score` (the documented way to bound semantic results).
- Fix `vfs.rename()` on a directory: child path updates spread the entity vector into `update()`
  and failed dimension validation; they are metadata-only updates now.
- Fix `vfs.move()`: copy+delete orphaned the content-addressed content blob (the destination
  shared the source hash, then unlink removed it). `move()` now delegates to `rename()` — an
  in-place path change that preserves the blob and the entity id, for files and directories.
- Fix streaming import: the bulk fast path never flushed mid-import nor signalled queryability.
  Entity writes are now chunked by a progressive flush interval (100 → 1000 → 5000); each chunk
  flushes and emits `progress.queryable`, so imported data is queryable during the import.
- Sweep all docs, comments, and JSDoc for the removed/changed APIs.

Integration suite: 49 files / 588 passed / 0 failed. Unit: 80 files / 1456 passed, no type errors.

docs/guides/import-flow.md

@@ -1707,12 +1707,12 @@ Brainy 8.0 ships two adapters: filesystem and memory.
 const brain = await Brainy.create({
   storage: {
     type: 'filesystem',
-    rootDirectory: './.brainy'
+    path: './.brainy'
   }
 })
 ```
 
-For off-site backup, snapshot `rootDirectory` from your scheduler with `gsutil rsync`, `aws s3 sync`, `rclone`, or `tar`. Brainy itself doesn't reach out to object storage.
+For off-site backup, snapshot `path` from your scheduler with `gsutil rsync`, `aws s3 sync`, `rclone`, or `tar`. Brainy itself doesn't reach out to object storage.
 
 ---
 
@@ -1743,7 +1743,7 @@ For off-site backup, snapshot `rootDirectory` from your scheduler with `gsutil r
 - HNSW Index: O(log n) search (1B entities = ~30 hops)
 - Metadata Index: O(1) filtering
 - Graph Adjacency: O(1) relationship lookups
-- Storage: Bounded by the filesystem volume backing `rootDirectory`
+- Storage: Bounded by the filesystem volume backing `path`
 
 ### Optimization Tips