PDF Text editor (#4724)

## Summary
- add a `PdfJsonConversionService` that serializes PDF text, fonts, and
metadata to JSON and rebuilds a PDF from the same structure
- expose REST endpoints for `/pdf/json` and `/json/pdf` conversions
using the existing convert API infrastructure
- define JSON model classes capturing document metadata, font
information, and positioned text elements

## Testing
- `./gradlew spotlessApply` *(fails: plugin
org.springframework.boot:3.5.4 unavailable in build environment)*
- `./gradlew build` *(fails: plugin org.springframework.boot:3.5.4
unavailable in build environment)*

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https://chatgpt.com/codex/tasks/task_b_68f8e98d94ac8328a0e499e541528b6f

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Co-authored-by: EthanHealy01 <[email protected]>

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

@@ -174,6 +174,23 @@ system:
   databaseBackup:
     cron: '0 0 0 * * ?' # Cron expression for automatic database backups "0 0 0 * * ?" daily at midnight
 
+stirling:
+  pdf:
+    fallback-font: classpath:/static/fonts/NotoSans-Regular.ttf # Override to point at a custom fallback font
+    json:
+      font-normalization:
+        enabled: false # IMPORTANT: Disable to preserve ToUnicode CMaps for correct font rendering. Ghostscript strips Unicode mappings from CID fonts.
+      cff-converter:
+        enabled: true # Wrap CFF/Type1C fonts as OpenType-CFF for browser compatibility
+        method: python # Converter method: 'python' (fontTools, recommended - wraps as OTF), 'fontforge' (legacy - converts to TTF, may hang on CID fonts)
+        python-command: /opt/venv/bin/python3 # Python interpreter path
+        python-script: /scripts/convert_cff_to_ttf.py # Path to font wrapping script
+        fontforge-command: fontforge # Override if FontForge is installed under a different name/path
+      type3:
+        library:
+          enabled: true # Match common Type3 fonts against the built-in library of converted programs
+          index: classpath:/type3/library/index.json # Override to point at a custom index.json (supports http:, file:, classpath:)
+
 ui:
   appNameNavbar: '' # name displayed on the navigation bar
   logoStyle: classic # Options: 'classic' (default - classic S icon) or 'modern' (minimalist logo)