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/embeddings/EmbeddingManager.ts

@@ -14,6 +14,7 @@
 
 import { Vector, EmbeddingFunction } from '../coreTypes.js'
 import { WASMEmbeddingEngine } from './wasm/index.js'
+import { isBrowser } from '../utils/environment.js'
 
 // Types
 export type ModelPrecision = 'q8' | 'fp32'
@@ -115,6 +116,9 @@ export class EmbeddingManager {
     const startTime = Date.now()
 
     try {
+      if (isBrowser()) {
+        console.warn('[brainy] Browser WASM embedding engine is deprecated and will be removed in v8.0. Use Node.js/Bun with native embeddings (@soulcraft/brainy-cortex) instead.')
+      }
       // Initialize WASM engine (handles all model loading)
       await this.engine.initialize()