merge(frontend): resolve conflicts with main — integrate fileHash feature into panel architecture

Keep the new bottom-panel / AnnotationSidePanel architecture from this branch
while pulling in the documentFileHash / visibleAnnotations filter that was added
on main. Thread documentFileHash through DocumentViewer so outdated-annotation
filtering works end-to-end.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/DocumentViewer.svelte

@@ -6,6 +6,7 @@ type Doc = {
 	id: string;
 	filePath?: string | null;
 	contentType?: string | null;
+	fileHash?: string | null;
 };
 
 type Props = {
@@ -83,6 +84,7 @@ let {
 			bind:activeAnnotationId={activeAnnotationId}
 			bind:activeAnnotationPage={activeAnnotationPage}
 			onAnnotationClick={onAnnotationClick}
+			documentFileHash={doc.fileHash ?? null}
 		/>
 	{:else if fileUrl}
 		<div class="flex h-full w-full items-center justify-center overflow-auto p-8">