feat(frontend): Upgrade embedPDF to v2.6.0 and migrate to pdf-lib fork, fix attachment/bookmark panel (#5723)

# Description of Changes

Upgrades embedPDF from v2.5.0 to v2.6.0 and migrates from unmaintained
pdf-lib to @cantoo/pdf-lib fork. Adds defensive error handling for
malformed PDFs and improves bridge lifecycle management.

### Changes

**Dependencies**
- Upgrade all @embedpdf/* packages from ^2.5.0 to ^2.6.0
- Replace pdf-lib with @cantoo/pdf-lib (maintained fork with better
TypeScript support)

**PDF Viewer Infrastructure (attachment/bookmark fix)**
- Add useDocumentReady hook to track document lifecycle across bridges
- Implement defensive bridge cleanup to prevent stale registrations
- Fix race condition in document ready state detection by subscribing to
events before checking state

**Link Extraction (updated to cantoo/pdf-lib)**
- Add graceful error handling for PDFs with invalid catalog structures
- Extract enhanced link metadata (tooltips, colors, border styles,
highlight modes)
- Return empty results instead of throwing on malformed PDFs
- Add validation for link creation (destination page bounds, rect
dimensions, color values)

**Signature Flattening  (updated to cantoo/pdf-lib)**
- Improve SVG embedding with three-tier fallback strategy (native
vector, rasterized PNG, placeholder)
- Add proper Unicode handling for PDF form tooltips via
PDFString.decodeText()
- Extract SVG utilities into cleaner strategy pattern

**Form Field Processing  (updated to cantoo/pdf-lib)**
- Add support for display labels vs export values in dropdown/list
fields per PDF spec 12.7.4.4
- Implement caching for expensive field property lookups
- Add proper handling of malformed /Opt arrays


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- Why the change was made
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## Checklist

### General

- [X] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [X] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [X] I have performed a self-review of my own code
- [X] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [X] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Signed-off-by: Balázs Szücs <[email protected]>

frontend/src/core/components/viewer/LocalEmbedPDF.tsx

@@ -125,7 +125,7 @@ export function LocalEmbedPDF({ file, url, fileName, enableAnnotations = false,
       }),
       createPluginRegistration(ScrollPluginPackage),
       createPluginRegistration(RenderPluginPackage, {
-        withForms: !enableFormFill, // Disable native form rendering when our interactive overlay is active
+        withForms: true,
         withAnnotations: showBakedAnnotations && !enableAnnotations, // Show baked annotations only when: visibility is ON and annotation layer is OFF
       }),
 
@@ -204,7 +204,7 @@ export function LocalEmbedPDF({ file, url, fileName, enableAnnotations = false,
       // Register print plugin for printing PDFs
       createPluginRegistration(PrintPluginPackage),
     ];
-  }, [pdfUrl, enableAnnotations, enableFormFill, showBakedAnnotations, fileName, file, url]);
+  }, [pdfUrl, enableAnnotations, showBakedAnnotations, fileName, file, url]);
 
   // Initialize the engine with the React hook - use local WASM for offline support
   const { engine, isLoading, error } = usePdfiumEngine({