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/index.ts

@@ -38,6 +38,18 @@ const app = Fastify({
   bodyLimit: env.MAX_UPLOAD_SIZE_MB * 1024 * 1024,
 });
 
+app.setErrorHandler((error: Error & { statusCode?: number }, request, reply) => {
+  const statusCode = error.statusCode ?? 500;
+  request.log.error(
+    { err: error, url: request.url, method: request.method },
+    "Unhandled request error",
+  );
+  reply.status(statusCode).send({
+    error: statusCode >= 500 ? "Internal server error" : error.message,
+    details: error.stack ?? error.message,
+  });
+});
+
 // Plugins
 await app.register(cors, {
   origin: env.CORS_ORIGIN