feat: add Phase 4 AI tools with Python bridge and 6 new tools

Add Python bridge (packages/ai/src/bridge.ts) that calls Python scripts
via child_process with venv-first fallback to system python3. Implements
6 AI-powered tools:

- Remove Background: rembg-based with U2-Net/IS-Net models
- Image Upscaling: Real-ESRGAN with Lanczos fallback
- OCR/Text Extraction: Tesseract + PaddleOCR engines
- Face/PII Blur: MediaPipe face detection with configurable blur
- Object Eraser: LaMa inpainting with mask-based input
- Smart Crop: Sharp attention-based entropy cropping (no Python needed)

Each tool includes: Python script, TypeScript wrapper, API route,
and React settings component. All Python scripts handle ImportError
gracefully with clear installation messages.

apps/api/package.json

@@ -17,6 +17,7 @@
     "@fastify/static": "^8.1.0",
     "@fastify/swagger": "^9.4.0",
     "@fastify/swagger-ui": "^5.2.0",
+    "@stirling-image/ai": "workspace:*",
     "@stirling-image/image-engine": "workspace:*",
     "@stirling-image/shared": "workspace:*",
     "archiver": "^7.0.1",