fix: remove dead model config code for true zero-config

- Remove unused model.type validation that caused Workshop error
- Remove model config from BrainyConfig type (never used)
- Simplify modelAutoConfig.ts (always Q8 WASM)
- Clean up zeroConfig.ts model references

This fixes the "Invalid model type: balanced" error and removes
unnecessary configuration options that did nothing.

src/types/brainy.types.ts

@@ -632,14 +632,7 @@ export interface BrainyConfig {
     options?: any
     branch?: string              // COW branch name (default: 'main')
   }
-  
-  // Model configuration
-  model?: {
-    type: 'fast' | 'accurate' | 'balanced' | 'custom'
-    name?: string           // Custom model name
-    precision?: 'q8'
-  }
-  
+
   // Index configuration
   index?: {
     m?: number              // HNSW M parameter