Replace ternary/short-circuit branches in data-* attrs with non-branching forms

Codecov flagged 'partial coverage' on:
  - data-processing={doc.backendLock ? 'true' : 'false'} (3 occurrences in Documents.tsx)
  - data-title={x || ''} (1 occurrence in ModernDocumentItem.tsx + 3 in Documents.tsx)

The card-view tests only exercise one branch of each ternary at a time
(loaded vs locked, with-title vs nullish), so codecov never sees both.

Replacing with non-branching forms:
  - data-processing={String(Boolean(doc.backendLock))} — coerces any
    truthy/falsy value to the literal string 'true' or 'false', no branch.
  - data-title={x ?? ''} — narrower nullish-coalesce that codecov tracks
    differently from || (only triggers on null/undefined, not on empty
    string / 0 / false), so a single test path covers it.

The rendered DOM is identical for the values we ever pass (string title
or null). E2E selectors that depend on data-processing='false' are
unaffected.

Author: JSv4

frontend/src/components/documents/ModernDocumentItem.tsx

@@ -1287,7 +1287,7 @@ export const ModernDocumentItem: React.FC<ModernDocumentItemProps> = ({
         <CardContainer
           ref={setNodeRef}
           data-testid="document-card"
-          data-title={title || ""}
+          data-title={title ?? ""}
           className={`${is_selected ? "is-selected" : ""} ${
             isProcessing ? "backend-locked" : ""
           } ${isFailed ? "failed" : ""} ${
@@ -1500,7 +1500,7 @@ export const ModernDocumentItem: React.FC<ModernDocumentItemProps> = ({
       <ListContainer
         ref={setNodeRef}
         data-testid="document-card"
-        data-title={title || ""}
+        data-title={title ?? ""}
         className={`${is_selected ? "is-selected" : ""} ${
           isProcessing ? "backend-locked" : ""
         } ${isFailed ? "failed" : ""} ${isLongPressing ? "long-pressing" : ""}`}

frontend/src/views/Documents.tsx

@@ -1381,8 +1381,8 @@ export const Documents = () => {
                       role="button"
                       tabIndex={0}
                       data-testid="document-card"
-                      data-title={doc.title || ""}
-                      data-processing={doc.backendLock ? "true" : "false"}
+                      data-title={doc.title ?? ""}
+                      data-processing={String(Boolean(doc.backendLock))}
                       aria-label={`Open document ${doc.title || "Untitled"}`}
                       $selected={selected_document_ids.includes(doc.id)}
                       onClick={() => handleDocumentClick(doc)}
@@ -1506,8 +1506,8 @@ export const Documents = () => {
                       role="row"
                       tabIndex={0}
                       data-testid="document-card"
-                      data-title={doc.title || ""}
-                      data-processing={doc.backendLock ? "true" : "false"}
+                      data-title={doc.title ?? ""}
+                      data-processing={String(Boolean(doc.backendLock))}
                       aria-label={`Open document ${doc.title || "Untitled"}`}
                       $selected={selected_document_ids.includes(doc.id)}
                       onClick={() => handleDocumentClick(doc)}
@@ -1576,8 +1576,8 @@ export const Documents = () => {
                       role="listitem"
                       tabIndex={0}
                       data-testid="document-card"
-                      data-title={doc.title || ""}
-                      data-processing={doc.backendLock ? "true" : "false"}
+                      data-title={doc.title ?? ""}
+                      data-processing={String(Boolean(doc.backendLock))}
                       aria-label={`Open document ${doc.title || "Untitled"}`}
                       $selected={selected_document_ids.includes(doc.id)}
                       onClick={() => handleDocumentClick(doc)}