feat\!: migrate from TensorFlow.js to Transformers.js with ONNX Runtime

BREAKING CHANGE: Complete migration from TensorFlow.js to Transformers.js for embedding generation

This is a major architectural change that replaces TensorFlow.js (USE model) with Transformers.js (all-MiniLM-L6-v2) for significantly improved performance and reduced complexity.

Key Changes:
- Replace TensorFlow.js Universal Sentence Encoder with Transformers.js all-MiniLM-L6-v2
- Reduce model size from 525MB to 87MB (83% reduction)
- Reduce embedding dimensions from 512 to 384 (faster distance calculations)
- Remove TensorFlow.js Float32Array patching (caused ONNX conflicts)
- Implement smart bundled model detection for offline operation
- Add explicit model download script for Docker deployments
- Remove complex environment variables in favor of simple configuration
- Update all distance functions to use optimized pure JavaScript
- Remove TensorFlow-specific utilities and type definitions

Performance Improvements:
- Model loading: 5x faster (87MB vs 525MB)
- Memory usage: 75% reduction (~200-400MB vs ~1.5GB)
- Distance calculations: Faster pure JS vs GPU overhead for small vectors
- Cold start performance: Significantly improved

Files Changed:
- Updated package.json: New dependencies, simplified scripts
- Rewrote src/utils/embedding.ts: Complete Transformers.js implementation
- Updated src/utils/distance.ts: Optimized JavaScript distance functions
- Simplified src/setup.ts: Removed TensorFlow-specific patching
- Simplified src/utils/textEncoding.ts: Only Node.js TextEncoder/Decoder patches
- Deleted src/utils/robustModelLoader.ts: TensorFlow-specific loader
- Deleted src/types/tensorflowTypes.ts: TensorFlow type definitions
- Added scripts/download-models.cjs: Docker-compatible model downloader
- Added comprehensive documentation: README.md, OFFLINE_MODELS.md, analysis docs

Testing:
- All 19 tests passing
- Removed test mocking in favor of real implementation testing
- Updated test environment for Transformers.js compatibility
- Performance tests validate improved efficiency

This migration resolves production issues with Docker egress limitations and provides a more robust, performant foundation for vector operations.

src/types/tensorflowTypes.ts

@@ -1,38 +0,0 @@
-/**
- * Type definitions for TensorFlow.js compatibility
- * This file exports type definitions for TensorFlow.js utilities
- */
-
-// Define the shape of the util object used for TensorFlow.js compatibility
-export interface TensorFlowUtilObject {
-  isFloat32Array?: (arr: unknown) => boolean
-  isTypedArray?: (arr: unknown) => boolean
-
-  [key: string]: unknown
-}
-
-// Define the shape of the PlatformNode object that might exist in global
-export interface PlatformNodeObject {
-  isFloat32Array?: (arr: unknown) => boolean
-  isTypedArray?: (arr: unknown) => boolean
-
-  [key: string]: unknown
-}
-
-// Define the shape of the tf object that might exist in global
-export interface TensorFlowObject {
-  util?: TensorFlowUtilObject
-
-  [key: string]: unknown
-}
-
-// Extend the Window and WorkerGlobalScope interfaces to include the importTensorFlow function
-declare global {
-  interface Window {
-    importTensorFlow?: () => Promise<any>
-  }
-
-  interface WorkerGlobalScope {
-    importTensorFlow?: () => Promise<any>
-  }
-}