feat: add backend API endpoints for highlights and cross-references

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

app/api/bible/cross-references/route.ts

@@ -0,0 +1,33 @@
+import { NextResponse } from 'next/server'
+import { prisma } from '@/lib/db'
+
+export const runtime = 'nodejs'
+
+export async function GET(request: Request) {
+  try {
+    const { searchParams } = new URL(request.url)
+    const verseId = searchParams.get('verseId')
+
+    if (!verseId) {
+      return NextResponse.json(
+        { error: 'verseId parameter required' },
+        { status: 400 }
+      )
+    }
+
+    // For now, return empty cross-references
+    // TODO: Implement actual cross-reference lookup in Phase 2.1B
+    // This would require a cross_references table mapping verses to related verses
+
+    return NextResponse.json({
+      verseId,
+      references: []
+    })
+  } catch (error) {
+    console.error('Error fetching cross-references:', error)
+    return NextResponse.json(
+      { error: 'Failed to fetch cross-references' },
+      { status: 500 }
+    )
+  }
+}