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

src/storage/storageFactory.ts

@@ -480,6 +480,7 @@ export async function createStorage(
         return memStorage
 
       case 'opfs': {
+        console.warn('[brainy] OPFS storage is deprecated and will be removed in v8.0. Migrate to Node.js/Bun with filesystem or mmap-filesystem storage.')
         // Check if OPFS is available
         const opfsStorage = new OPFSStorage()
         if (opfsStorage.isOPFSAvailable()) {
@@ -839,6 +840,7 @@ export async function createStorage(
 
   // Next, try OPFS (browser only)
   if (isBrowser()) {
+    console.warn('[brainy] Browser environment detected. Browser support is deprecated and will be removed in v8.0. Migrate to Node.js/Bun.')
     const opfsStorage = new OPFSStorage()
     if (opfsStorage.isOPFSAvailable()) {
       console.log('Using OPFS storage (auto-detected) + TypeAware wrapper')