feat(crop): improve UI and fix batch crop for multi-file

- Replace Rule of Thirds button with checkbox for clearer toggle
- Show side-by-side comparison after crop instead of overlay slider
- Add custom aspect ratio option with W:H number inputs
- Fix batch crop failing on files with different dimensions by
  sending percentage-based coordinates instead of absolute pixels
- Add failed-file error state display in tool page

apps/api/src/routes/tools/crop.ts

@@ -6,10 +6,11 @@ import { resolveOutputFormat } from "../../lib/output-format.js";
 import { createToolRoute } from "../tool-factory.js";
 
 const settingsSchema = z.object({
-  left: z.number().int().min(0),
-  top: z.number().int().min(0),
-  width: z.number().int().positive(),
-  height: z.number().int().positive(),
+  left: z.number().min(0),
+  top: z.number().min(0),
+  width: z.number().positive(),
+  height: z.number().positive(),
+  unit: z.enum(["px", "percent"]).optional(),
 });
 
 export function registerCrop(app: FastifyInstance) {