OCR fix and Mobile QR changes (#5433)

# Description of Changes
## OCR / Tesseract path handling

Makes tessDataPath resolution deterministic with priority: config >
TESSDATA_PREFIX env > default.
Updates language discovery to use runtimePathConfig.getTessDataPath()
instead of raw config value.
Ensure default OCR dir is debian based not alpine

## Mobile scanner: feature gating + new conversion settings
Adds system.mobileScannerSettings (convert-to-PDF + resolution + page
format + stretch) exposed via backend config and configurable in the
proprietary admin UI.
Enforces enableMobileScanner on the MobileScannerController endpoints
(403 when disabled).
Frontend mobile upload flow can now optionally convert received images
to PDF (pdf-lib + canvas).

## Desktop/Tauri connectivity work
Expands tauri-plugin-http permissions and enables dangerous-settings.
Adds a very comprehensive multi-stage server connection diagnostic
routine (with lots of logging).


<img width="688" height="475" alt="image"
src="https://github.com/user-attachments/assets/6f9c1aec-58c7-449b-96b0-52f25430d741"
/>


---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(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](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### 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 tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

app/core/src/main/resources/settings.yml.template

@@ -146,6 +146,11 @@ system:
   backendUrl: '' # Backend base URL for SAML/OAuth/API callbacks (e.g. 'http://localhost:8080' for dev, 'https://api.example.com' for production). REQUIRED for SSO authentication to work correctly. This is where your IdP will send SAML responses and OAuth callbacks. Leave empty to default to 'http://localhost:8080' in development.
   frontendUrl: '' # Frontend URL for invite email links (e.g. 'https://app.example.com'). Optional - if not set, will use backendUrl. This is the URL users click in invite emails.
   enableMobileScanner: false # Enable mobile phone QR code upload feature. Requires frontendUrl to be configured.
+  mobileScannerSettings:
+    convertToPdf: true # Automatically convert uploaded images to PDF format. If false, images are kept as-is.
+    imageResolution: full # Image resolution for mobile uploads: 'full' (original size) or 'reduced' (max 1200px on longest side). Only applies when convertToPdf is true.
+    pageFormat: A4 # Page format for converted PDFs: 'keep' (original image dimensions), 'A4' (A4 page size), or 'letter' (US Letter page size). Only applies when convertToPdf is true.
+    stretchToFit: false # Whether to stretch images to fill the entire page (may distort aspect ratio). If false, images are centered with preserved aspect ratio. Only applies when convertToPdf is true.
   serverCertificate:
     enabled: true # Enable server-side certificate for "Sign with Stirling-PDF" option
     organizationName: Stirling-PDF # Organization name for generated certificates