fix: enable GCS native storage with Application Default Credentials

This fixes critical bugs that completely blocked GCS native storage from working:

1. Type validation rejected 'gcs-native' as invalid storage type
2. TypeScript type definition didn't include 'gcs-native'
3. Auto-detection returned S3-compatible GCS instead of native SDK
4. No validation for type/config mismatches (gcs vs gcs-native)

Changes:
- Add 'gcs-native' to storage type validation array (src/brainy.ts)
- Add GCS_NATIVE enum value to StorageType (src/config/storageAutoConfig.ts)
- Add 'gcs-native' to StorageTypeString type union (src/config/storageAutoConfig.ts)
- Change auto-detection to use native GCS SDK with ADC instead of S3-compatible (src/config/storageAutoConfig.ts)
- Add helpful validation to catch type/config mismatches (src/brainy.ts)

Impact:
- GCS native storage now works as documented
- Cloud Run deployments can use Application Default Credentials
- Auto-detection correctly selects native adapter in GCP environments
- Clear error messages guide users when they mix up gcs vs gcs-native

Fixes production blocker for teams deploying on Google Cloud Platform.

src/brainy.ts

@@ -2666,8 +2666,31 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    */
   private normalizeConfig(config?: BrainyConfig): Required<BrainyConfig> {
     // Validate storage configuration
-    if (config?.storage?.type && !['auto', 'memory', 'filesystem', 'opfs', 'remote', 's3', 'r2', 'gcs'].includes(config.storage.type)) {
-      throw new Error(`Invalid storage type: ${config.storage.type}. Must be one of: auto, memory, filesystem, opfs, remote, s3, r2, gcs`)
+    if (config?.storage?.type && !['auto', 'memory', 'filesystem', 'opfs', 'remote', 's3', 'r2', 'gcs', 'gcs-native'].includes(config.storage.type)) {
+      throw new Error(`Invalid storage type: ${config.storage.type}. Must be one of: auto, memory, filesystem, opfs, remote, s3, r2, gcs, gcs-native`)
+    }
+
+    // Validate storage type/config pairing (catch common mismatches)
+    if (config?.storage) {
+      const storage = config.storage as any
+
+      // Check for gcs/gcsNativeStorage mismatch
+      if (storage.type === 'gcs' && storage.gcsNativeStorage) {
+        throw new Error(
+          `Storage type/config mismatch: type 'gcs' requires 'gcsStorage' config object (S3-compatible). ` +
+          `You provided 'gcsNativeStorage' which requires type 'gcs-native'. ` +
+          `Either change type to 'gcs-native' or use 'gcsStorage' instead of 'gcsNativeStorage'.`
+        )
+      }
+
+      // Check for gcs-native/gcsStorage mismatch
+      if (storage.type === 'gcs-native' && storage.gcsStorage) {
+        throw new Error(
+          `Storage type/config mismatch: type 'gcs-native' requires 'gcsNativeStorage' config object. ` +
+          `You provided 'gcsStorage' which requires type 'gcs' (S3-compatible). ` +
+          `Either change type to 'gcs' or use 'gcsNativeStorage' instead of 'gcsStorage'.`
+        )
+      }
     }
 
     // Validate model configuration

src/config/storageAutoConfig.ts

@@ -10,10 +10,11 @@ import { isBrowser, isNode } from '../utils/environment.js'
  */
 export enum StorageType {
   MEMORY = 'memory',
-  FILESYSTEM = 'filesystem', 
+  FILESYSTEM = 'filesystem',
   OPFS = 'opfs',
   S3 = 's3',
   GCS = 'gcs',
+  GCS_NATIVE = 'gcs-native',
   R2 = 'r2'
 }
 
@@ -28,7 +29,7 @@ export enum StoragePreset {
 }
 
 // Backward compatibility type aliases
-export type StorageTypeString = 'memory' | 'filesystem' | 'opfs' | 's3' | 'gcs' | 'r2'
+export type StorageTypeString = 'memory' | 'filesystem' | 'opfs' | 's3' | 'gcs' | 'r2' | 'gcs-native'
 export type StoragePresetString = 'auto' | 'memory' | 'disk' | 'cloud'
 
 export interface StorageConfigResult {
@@ -197,14 +198,14 @@ async function detectCloudStorage(): Promise<{ type: StorageType; config: any }
     }
   }
   
-  // Google Cloud Storage Detection
+  // Google Cloud Storage Detection (Native SDK with ADC)
   if (hasGCPConfig()) {
     return {
-      type: StorageType.GCS,
+      type: StorageType.GCS_NATIVE,
       config: {
-        gcsStorage: {
+        gcsNativeStorage: {
           bucketName: process.env.GCS_BUCKET || process.env.GOOGLE_STORAGE_BUCKET || 'brainy-data',
-          // Credentials will be picked up by GCP SDK automatically
+          // Application Default Credentials will be picked up automatically
         }
       }
     }