feat: implement clean embedding architecture with Q8/FP32 precision control

- Unified embedding system with single EmbeddingManager
- Q8 model support with 75% smaller footprint (23MB vs 90MB)
- Intelligent precision auto-selection based on environment
- Clean cached embeddings with TTL and memory management
- Zero-config setup with smart defaults
- Complete storage structure documentation
- Removed legacy worker and hybrid managers
- Streamlined model configuration and precision management

src/config/zeroConfig.ts

@@ -78,7 +78,7 @@ const PRESETS = {
   },
   development: {
     storage: 'memory' as const,
-    model: 'fp32' as const,
+    model: 'q8' as const,  // Q8 is now the default for all presets
     features: 'full' as const,
     verbose: true
   },