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


<!--
Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
-->

---

## 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/SignatureAPIBridge.tsx

@@ -5,6 +5,11 @@ import { useSignature } from '@app/contexts/SignatureContext';
 import type { SignatureAPI } from '@app/components/viewer/viewerTypes';
 import type { SignParameters } from '@app/hooks/tools/sign/useSignParameters';
 import { useViewer } from '@app/contexts/ViewerContext';
+import { useDocumentReady } from '@app/components/viewer/hooks/useDocumentReady';
+
+/**
+ * Connects the PDF signature (stamp/ink) tools to the shared ViewerContext and SignatureContext.
+ */
 
 // Minimum allowed width/height (in pixels) for a signature image or text stamp.
 // This prevents rendering issues and ensures signatures are always visible and usable.
@@ -132,6 +137,7 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
   const { provides: annotationApi } = useAnnotationCapability();
   const { signatureConfig, storeImageData, isPlacementMode, placementPreviewSize, setSignaturesApplied } = useSignature();
   const { getZoomState, registerImmediateZoomUpdate } = useViewer();
+  const documentReady = useDocumentReady();
   const [currentZoom, setCurrentZoom] = useState(() => getZoomState()?.currentZoom ?? 1);
   const lastStampImageRef = useRef<string | null>(null);
 
@@ -211,7 +217,7 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
   // Enable keyboard deletion of selected annotations
   useEffect(() => {
     // Always enable delete key when we have annotation API and are in sign mode
-    if (!annotationApi || (isPlacementMode === undefined)) return;
+    if (!annotationApi || (isPlacementMode === undefined) || !documentReady) return;
 
     const handleKeyDown = (event: KeyboardEvent) => {
       // Skip delete/backspace while a text input/textarea is focused (e.g., editing textbox)
@@ -391,7 +397,7 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
   }), [annotationApi, signatureConfig, placementPreviewSize, applyStampDefaults]);
 
   useEffect(() => {
-    if (!annotationApi?.onAnnotationEvent) {
+    if (!annotationApi?.onAnnotationEvent || !documentReady) {
       return;
     }
 
@@ -430,10 +436,10 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
     return () => {
       unsubscribe?.();
     };
-  }, [annotationApi, storeImageData, setSignaturesApplied]);
+  }, [annotationApi, storeImageData, setSignaturesApplied, documentReady]);
 
   useEffect(() => {
-    if (!isPlacementMode) {
+    if (!isPlacementMode || !documentReady) {
       return;
     }
 
@@ -447,66 +453,7 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
     return () => {
       cancelled = true;
     };
-  }, [isPlacementMode, configureStampDefaults, placementPreviewSize, signatureConfig]);
-
-  useEffect(() => {
-    if (!annotationApi?.onAnnotationEvent) {
-      return;
-    }
-
-    const unsubscribe = annotationApi.onAnnotationEvent(event => {
-      if (event.type !== 'create' && event.type !== 'update') {
-        return;
-      }
-
-      const annotation: any = event.annotation;
-      const annotationId: string | undefined = annotation?.id;
-      if (!annotationId) {
-        return;
-      }
-
-      // Mark signatures as not applied when a new signature is placed
-      if (event.type === 'create') {
-        setSignaturesApplied(false);
-      }
-
-      const directData =
-        extractDataUrl(annotation.imageSrc) ||
-        extractDataUrl(annotation.imageData) ||
-        extractDataUrl(annotation.appearance) ||
-        extractDataUrl(annotation.stampData) ||
-        extractDataUrl(annotation.contents) ||
-        extractDataUrl(annotation.data) ||
-        extractDataUrl(annotation.customData) ||
-        extractDataUrl(annotation.asset);
-
-      const dataToStore = directData || lastStampImageRef.current;
-      if (dataToStore) {
-        storeImageData(annotationId, dataToStore);
-      }
-    });
-
-    return () => {
-      unsubscribe?.();
-    };
-  }, [annotationApi, storeImageData, setSignaturesApplied]);
-
-  useEffect(() => {
-    if (!isPlacementMode) {
-      return;
-    }
-
-    let cancelled = false;
-    configureStampDefaults().catch((error) => {
-      if (!cancelled) {
-        console.error('Error updating signature defaults:', error);
-      }
-    });
-
-    return () => {
-      cancelled = true;
-    };
-  }, [isPlacementMode, configureStampDefaults, placementPreviewSize, signatureConfig]);
+  }, [isPlacementMode, configureStampDefaults, placementPreviewSize, signatureConfig, documentReady]);
 
 
   return null; // This is a bridge component with no UI