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/src/routes/tools/smart-crop.ts

@@ -0,0 +1,33 @@
+import { z } from "zod";
+import sharp from "sharp";
+import type { FastifyInstance } from "fastify";
+import { createToolRoute } from "../tool-factory.js";
+
+const settingsSchema = z.object({
+  width: z.number().int().positive(),
+  height: z.number().int().positive(),
+});
+
+/**
+ * Smart crop using Sharp's attention-based strategy.
+ * Uses entropy/saliency detection to find the most interesting region.
+ * No Python needed.
+ */
+export function registerSmartCrop(app: FastifyInstance) {
+  createToolRoute(app, {
+    toolId: "smart-crop",
+    settingsSchema,
+    process: async (inputBuffer, settings, filename) => {
+      const result = await sharp(inputBuffer)
+        .resize(settings.width, settings.height, {
+          fit: "cover",
+          position: sharp.strategy.attention,
+        })
+        .png()
+        .toBuffer();
+
+      const outputFilename = filename.replace(/\.[^.]+$/, "") + "_smartcrop.png";
+      return { buffer: result, filename: outputFilename, contentType: "image/png" };
+    },
+  });
+}