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.

packages/ai/python/remove_bg.py

@@ -0,0 +1,47 @@
+"""Background removal using rembg."""
+import sys
+import json
+
+
+def main():
+    input_path = sys.argv[1]
+    output_path = sys.argv[2]
+    settings = json.loads(sys.argv[3]) if len(sys.argv) > 3 else {}
+
+    model = settings.get("model", "u2net")
+
+    try:
+        from rembg import remove
+
+        with open(input_path, "rb") as f:
+            input_data = f.read()
+
+        output_data = remove(
+            input_data,
+            alpha_matting=True,
+            alpha_matting_foreground_threshold=240,
+            alpha_matting_background_threshold=10,
+        )
+
+        with open(output_path, "wb") as f:
+            f.write(output_data)
+
+        print(json.dumps({"success": True, "model": model}))
+
+    except ImportError:
+        print(
+            json.dumps(
+                {
+                    "success": False,
+                    "error": "rembg is not installed. Install with: pip install rembg[cpu]",
+                }
+            )
+        )
+        sys.exit(1)
+    except Exception as e:
+        print(json.dumps({"success": False, "error": str(e)}))
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()