feat: wire plugin system with provider resolution, storage factories, and browser deprecation

- Wire PluginRegistry into Brainy init() with provider resolution for distance,
  metadataIndex, graphIndex, embeddings, roaring, msgpack, and storage adapters
- Add setupStorage() factory that resolves storage:* providers from plugins before
  falling back to built-in createStorage()
- Export internals API (setGlobalCache, UnifiedCache, EntityIdMapper, etc.) for
  cortex plugin consumption
- Add plugin.test.ts verifying registration, activation, and provider resolution
- Deprecate browser support (OPFS, Web Workers, WASM embeddings) with warnings
  in preparation for v8.0 server-only release
- FileSystemStorage: fix setupStorage resolution for mmap-filesystem provider

package.json

@@ -51,6 +51,14 @@
     "./neural/SmartRelationshipExtractor": {
       "import": "./dist/neural/SmartRelationshipExtractor.js",
       "types": "./dist/neural/SmartRelationshipExtractor.d.ts"
+    },
+    "./plugin": {
+      "import": "./dist/plugin.js",
+      "types": "./dist/plugin.d.ts"
+    },
+    "./internals": {
+      "import": "./dist/internals.js",
+      "types": "./dist/internals.d.ts"
     }
   },
   "browser": {