fix: large document handling and Cassandra query pagination

- Paginate heavy Cassandra reads (triples, graph/document embeddings)
  using synchronous session.execute() in run_in_executor with fetch_size
  paging, preventing materialization hang on large result sets
- Fix document stream endpoint to use workspace-scoped librarian queues
- Add decoder error handling for PDF/OCR/unstructured processors
- Add WebSocket mux guards for missing auth fields
- Add null check in librarian document streaming
- Rewrite get_document_content CLI to stream via librarian
- Add Poppler dependency to unstructured container

trustgraph-flow/trustgraph/decoding/pdf/pdf_decoder.py

@@ -129,7 +129,15 @@ class Processor(FlowProcessor):
                 )
                 PyPDFLoader = _cls
             loader = PyPDFLoader(temp_path)
-            pages = loader.load()
+            try:
+                pages = loader.load()
+            except Exception as e:
+                source_doc_id = v.document_id or v.metadata.id
+                logger.error(
+                    f"Failed to decode PDF {source_doc_id}: "
+                    f"{type(e).__name__}: {e}"
+                )
+                return
 
             # Get the source document ID
             source_doc_id = v.document_id or v.metadata.id