refactor(8.0): delete DataAPI — superseded by Db persist/restore + import API + stats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

@@ -142,11 +142,11 @@ export const utilityCommands = {
 
       // Show warning before clearing
       console.log(chalk.yellow('\n⚠️  WARNING: This will permanently delete ALL data!'))
-      const dataApi = await brain.data()
 
-      // Clear all data
+      // Clear all data (entities, relationships, and every index)
       spinner.text = 'Clearing all data...'
-      await dataApi.clear({ entities: true, relations: true })
+      await brain.init()
+      await brain.clear()
 
       spinner.succeed('Database cleared')
 
@@ -156,6 +156,12 @@ export const utilityCommands = {
       } else {
         formatOutput({ cleared: true, success: true }, options)
       }
+
+      // close() releases the writer lock and indexes, but global timers
+      // (UnifiedCache bookkeeping, PathResolver stats) keep the event loop
+      // alive. CLI commands are one-shot — exit explicitly.
+      await brain.close()
+      process.exit(0)
     } catch (error: any) {
       spinner.fail('Cleanup failed')
       console.error(chalk.red(error.message))