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/batch.ts

@@ -13,6 +13,7 @@ import type { FastifyInstance, FastifyReply, FastifyRequest } from "fastify";
 import PQueue from "p-queue";
 import { env } from "../config.js";
 import { autoOrient } from "../lib/auto-orient.js";
+import { formatZodErrors } from "../lib/errors.js";
 import { validateImageBuffer } from "../lib/file-validation.js";
 import { sanitizeFilename } from "../lib/filename.js";
 import { decodeHeic } from "../lib/heic-converter.js";
@@ -88,12 +89,7 @@ export async function registerBatchRoutes(app: FastifyInstance): Promise<void> {
         if (!result.success) {
           return reply.status(400).send({
             error: "Invalid settings",
-            details: result.error.issues.map(
-              (i: { path: (string | number)[]; message: string }) => ({
-                path: i.path.join("."),
-                message: i.message,
-              }),
-            ),
+            details: formatZodErrors(result.error.issues),
           });
         }
         settings = result.data;