fix: verbose error handling, batch processing, and multi-file support

- Replace [object Object] errors with readable messages across all 20+ API
  routes by normalizing Zod validation errors to strings (formatZodErrors)
- Add parseApiError() on frontend to defensively handle any details type
- Add global Fastify error handler with full stack traces in logs
- Fix image-to-pdf auth: Object.entries(headers) → headers.forEach()
- Fix passport-photo: safeParse + formatZodErrors, safe error extraction
- Fix OCR silent fallbacks: log exception type/message when falling back,
  include actual engine used in API response and Docker logs
- Fix split tool: process all uploaded images, combine into ZIP with
  subfolders per image
- Fix batch support for blur-faces, strip-metadata, edit-metadata,
  vectorize: add processAllFiles branch for multi-file uploads
- Docker: LOG_LEVEL=debug, PYTHONWARNINGS=default for visibility
- Add Playwright e2e tests verifying all fixes against Docker container

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

@@ -5,6 +5,7 @@ import type { FastifyInstance } from "fastify";
 import sharp from "sharp";
 import { z } from "zod";
 import { autoOrient } from "../../lib/auto-orient.js";
+import { formatZodErrors } from "../../lib/errors.js";
 import { ensureSharpCompat } from "../../lib/heic-converter.js";
 
 const settingsSchema = z.object({
@@ -67,7 +68,9 @@ export function registerSplit(app: FastifyInstance) {
       const parsed = settingsRaw ? JSON.parse(settingsRaw) : {};
       const result = settingsSchema.safeParse(parsed);
       if (!result.success) {
-        return reply.status(400).send({ error: "Invalid settings", details: result.error.issues });
+        return reply
+          .status(400)
+          .send({ error: "Invalid settings", details: formatZodErrors(result.error.issues) });
       }
       settings = result.data;
     } catch {