feat: progressive init and readiness API for cloud storage

- Add `initMode` option to all cloud storage adapters (GCS, S3, Azure)
  - 'auto' (default): progressive in cloud, strict locally
  - 'progressive': <200ms cold starts, lazy bucket validation
  - 'strict': blocking validation (current behavior)

- Add cloud environment auto-detection for:
  - Cloud Run (K_SERVICE, K_REVISION)
  - AWS Lambda (AWS_LAMBDA_FUNCTION_NAME)
  - Cloud Functions (FUNCTIONS_TARGET)
  - Azure Functions (AZURE_FUNCTIONS_ENVIRONMENT)

- Add readiness API to Brainy class:
  - `brain.ready`: Promise that resolves when init() completes
  - `brain.isFullyInitialized()`: checks if background tasks done
  - `brain.awaitBackgroundInit()`: waits for background tasks

- Lazy bucket validation on first write (not during init)
- Background count synchronization
- Update AWS/GCP deployment docs with readiness patterns

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/types/brainyInterface.ts

@@ -17,6 +17,28 @@ export interface BrainyInterface<T = unknown> {
    */
   init(): Promise<void>
 
+  /**
+   * Promise that resolves when initialization is complete (v7.3.0+)
+   * Can be awaited multiple times safely.
+   */
+  readonly ready: Promise<void>
+
+  /**
+   * Check if basic initialization is complete
+   */
+  readonly isInitialized: boolean
+
+  /**
+   * Check if all initialization including background tasks is complete (v7.3.0+)
+   */
+  isFullyInitialized(): boolean
+
+  /**
+   * Wait for all background initialization tasks to complete (v7.3.0+)
+   * For cloud storage adapters, this waits for bucket validation and count sync.
+   */
+  awaitBackgroundInit(): Promise<void>
+
   /**
    * Modern add method - unified entity creation
    * @param params Parameters for adding entities