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/application.properties

@@ -1,5 +1,6 @@
 multipart.enabled=true
 logging.level.org.springframework=WARN
+logging.level.org.springframework.security=WARN
 logging.level.org.hibernate=WARN
 logging.level.org.eclipse.jetty=WARN
 #logging.level.org.springframework.security.oauth2=DEBUG
@@ -7,6 +8,9 @@ logging.level.org.eclipse.jetty=WARN
 #logging.level.org.opensaml=DEBUG
 #logging.level.stirling.software.proprietary.security=DEBUG
 logging.level.com.zaxxer.hikari=WARN
+logging.level.stirling.software.SPDF.service.PdfJsonConversionService=INFO
+logging.level.stirling.software.common.service.JobExecutorService=INFO
+logging.level.stirling.software.common.service.TaskManager=INFO
 spring.jpa.open-in-view=false
 server.forward-headers-strategy=NATIVE
 server.error.path=/error