refactor(8.0): delete DataAPI — superseded by Db persist/restore + import API + stats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

src/cli/index.ts

@@ -173,12 +173,6 @@ program
   .option('--skip-node-modules', 'Skip node_modules', true)
   .action(importCommands.import)
 
-program
-  .command('export [file]')
-  .description('Export database')
-  .option('-f, --format <format>', 'Output format (json|csv|jsonl)', 'json')
-  .action(coreCommands.export)
-
 program
   .command('diagnostics')
   .alias('diag')
@@ -549,11 +543,12 @@ program
 
 // ===== Data Management Commands =====
 
-
-program
 program
   .command('data-stats')
   .description('Show detailed database statistics')
+  .option('--verbose', 'List every indexed field name')
+  .option('--json', 'Output as JSON')
+  .option('--pretty', 'Pretty print JSON')
   .action(dataCommands.stats)
 
 // ===== Inspect Commands =====
@@ -764,7 +759,12 @@ program
 
 program
   .command('snapshot <path>')
-  .description('📸 Persist the current generation as a self-contained snapshot (instant hard links)')
+  .alias('export')
+  .description(
+    '📸 Persist the current generation as a self-contained snapshot (instant hard links). ' +
+      'A snapshot is the full-fidelity export format: open it with Brainy.load(path) or ' +
+      'load it wholesale with `brainy restore`. For ingesting external data files, see `brainy import`.'
+  )
   .action(snapshotCommands.snapshot)
 
 program