Add Auto Form Detection

[Frooodle]

Description of Changes

detection of form-field regions → fillable AcroForm. Runs in-browser (private) or on the server.

Feature

• New "Auto Form Detection" tool (Create → Forms).
• Two engines: in-browser (onnxruntime-web/WASM) and server (onnxruntime Java).
• Detect → review → apply, returns a fillable PDF.

Admin (Settings → Features → AI Form Detection)

• On/off master switch.
• Engine selector: Auto / Browser / Server (Server greys out if not bundled).
• Model catalog: install / switch / uninstall.
• Air-gapped install instructions per model.

Models

• CommonForms FFDNet-S (small, ~37MB) and FFDNet-L (large, ~97MB).
• Downloaded on demand + SHA-256 verified; cached in-browser via Cache API.
• License shown in-UI (YOLOv8/AGPL lineage; weights never redistributed).

Docker

• Feature enabled by default, model pre-bundled (FFDNet-S baked in, seeded into /configs on startup) - works out-of-the-box, no install step.
• Server ONNX engine bundled via -PbundleOnnxRuntime=true, slimmed to one Linux arch (~42MB → ~8MB).

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Checklist

General

• I have read the Contribution Guidelines
• I have read the Stirling-PDF Developer Guide (if applicable)
• I have read the How to add new languages to Stirling-PDF (if applicable)
• I have performed a self-review of my own code
• My changes generate no new warnings

Documentation

• I have updated relevant docs on Stirling-PDF's doc repo (if functionality has heavily changed)
• I have read the section Add New Translation Tags (for new translation tags only)

Translations (if applicable)

• I ran scripts/counter_translation.py

UI Changes (if applicable)

• Screenshots or videos demonstrating the UI changes are attached (e.g., as comments or direct attachments in the PR)

Testing (if applicable)

• I have run task check to verify linters, typechecks, and tests pass
• I have tested my changes locally. Refer to the Testing Guide for more details.

[github-actions]

Frontend Check Failed

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Run task frontend:fix to auto-fix what can be fixed automatically, then run task frontend:check:all to see what still needs fixing manually.

[stirlingbot]

✅ Frontend License Check Passed

All frontend licenses have been validated and no compatibility warnings were detected.

The frontend license report has been updated successfully.

[stirlingbot]

✅ Backend License Check Passed

All backend dependencies have valid and allowed licenses.

The backend license report has been updated successfully.

[stirlingbot]

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