refactor(8.0): delete DataAPI — superseded by Db persist/restore + import API + stats

The legacy backup/import/export/stats facade (src/api/DataAPI.ts) drifted
from the modern entity shape and every job it did now has a first-class
surface. Delete it and brain.data(), and rewire the CLI:

- data-stats → brain.stats() (full BrainyStats report: per-type breakdowns,
  indexed fields, index health, storage backend, writer lock, version)
- clean → brain.clear()
- export → alias of snapshot; a db.persist() snapshot is the full-fidelity
  export format (open with Brainy.load, load wholesale with brainy restore);
  external data ingestion remains brainy import (UniversalImportAPI)

Rewiring clean onto brain.clear() exposed two real bugs, both fixed:

- clear() left this.graphIndex undefined forever — any graph-touching call
  afterwards (relate, getNeighbors, stats) crashed. clear() now re-resolves
  the graph index exactly as init() does and re-wires the shared UUID↔int
  resolver, and re-resolves the metadata index with the same provider
  fallback as init().
- storage.clear() reset the legacy totals but not the per-type/subtype
  count rollups or id→type caches, so stats() reported phantom counts for
  deleted entities. Both adapters now delegate derived-state reset to
  reloadDerivedState(), the same path restore-from-snapshot uses.

One-shot CLI commands (data-stats, clean, snapshot/export, restore,
history, generation) now close the brain and exit explicitly — global
cache timers otherwise keep the process alive holding the writer lock.

Verified: build clean, 1383/1383 unit tests, 24/24 db-mvcc integration,
plus an end-to-end CLI smoke (add → data-stats → export → clean →
data-stats).

tests/unit/brainy-core.unit.test.ts

@@ -220,16 +220,18 @@ describe('Brainy 3.0 Core (Unit Tests)', () => {
         type: NounType.Concept
       })
       
-      // Clear using DataAPI
-      const dataAPI = await brain.data()
-      await dataAPI.clear({ entities: true, relations: false })
-      
-      // Verify data is cleared
-      const results = await brain.find({ 
+      // Clear everything — entities, relationships, and all indexes
+      await brain.clear()
+
+      // Verify user data is cleared. clear() re-creates a fresh VFS root
+      // entity, and a thresholdless vector search can surface it — so filter
+      // VFS bookkeeping out and assert the added entities are gone.
+      const results = await brain.find({
         query: 'Test',
-        limit: 10 
+        limit: 10
       })
-      expect(results.length).toBe(0)
+      const userResults = results.filter(r => !r.metadata?.isVFS)
+      expect(userResults.length).toBe(0)
     })
   })