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]>

docker/frontend/nginx.conf

@@ -24,7 +24,7 @@ http {
         index index.html index.htm;
         
         # Global settings for file uploads
-        client_max_body_size 100m;
+        client_max_body_size 0;
 
         # Handle client-side routing - support subpaths
         location / {
@@ -48,12 +48,12 @@ http {
             proxy_cache off;
             
             # Timeout settings for large file uploads
-            proxy_connect_timeout 60s;
-            proxy_send_timeout 60s;
-            proxy_read_timeout 60s;
-            
+            proxy_connect_timeout 600s;
+            proxy_send_timeout 600s;
+            proxy_read_timeout 600s;
+
             # Request size limits for file uploads
-            client_max_body_size 100m;
+            client_max_body_size 0;
             proxy_request_buffering off;
         }