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]>

frontend/src/proprietary/utils/urlMapping.ts

@@ -0,0 +1,19 @@
+/**
+ * Proprietary URL mappings.
+ * This file overrides src/core/utils/urlMapping.ts
+ * to add proprietary-specific URL mappings.
+ */
+
+import { ToolId } from '@app/types/toolId';
+import { URL_TO_TOOL_MAP as CORE_URL_TO_TOOL_MAP } from '@core/utils/urlMapping';
+
+// Proprietary URL mappings
+const PROPRIETARY_URL_MAPPINGS: Record<string, ToolId> = {
+  '/pdf-text-editor': 'pdfTextEditor',
+};
+
+// Merge core and proprietary mappings
+export const URL_TO_TOOL_MAP: Record<string, ToolId> = {
+  ...CORE_URL_TO_TOOL_MAP,
+  ...PROPRIETARY_URL_MAPPINGS,
+};