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/web/src/components/tools/erase-object-settings.tsx

@@ -111,7 +111,13 @@ export function EraseObjectSettings({
       } else {
         try {
           const body = JSON.parse(xhr.responseText);
-          setError(body.error || body.details || `Failed: ${xhr.status}`);
+          setError(
+            typeof body.error === "string"
+              ? body.error
+              : typeof body.details === "string"
+                ? body.details
+                : `Failed: ${xhr.status}`,
+          );
         } catch {
           setError(`Processing failed: ${xhr.status}`);
         }