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/proprietary/build.gradle

@@ -73,3 +73,11 @@ dependencies {
 }
 
 tasks.register('prepareKotlinBuildScriptModel') {}
+
+tasks.register('type3SignatureTool', JavaExec) {
+    group = 'type3'
+    description = 'Dump Type3 font signatures and glyph coverage for the Type3 library'
+    classpath = sourceSets.main.runtimeClasspath
+    mainClass = 'stirling.software.SPDF.service.pdfjson.type3.tool.Type3SignatureTool'
+    standardInput = System.in
+}