Production hardening: bounded parallel conversion and health sync

[DevBehindYou]

This PR continues the mdify-pro-rebuild line without introducing unnecessary microservices.

Changes:

• move blocking document conversion off the FastAPI event loop
• bound backend conversion concurrency with a configurable per-process cap (default 2)
• add bounded parallel batch conversion in the frontend
• guard against overlapping "Convert all" pools
• stop health polling once the backend is online
• validate the concurrency setting
• document the setting
• run CI for mdify-pro-rebuild as well as main

This preserves the existing converter/pipeline architecture and keeps a clean extraction path for future OCR/worker services.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
mdify	Error		Sep 6, 2026 4:51pm UTC
mdify-app	Ready	Preview	Sep 6, 2026 4:51pm UTC

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: ad869e11-a115-4a25-9b47-dbf1b86a0f46

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

_{Comment @coderabbitai help to get the list of available commands.}