Remove dedupeHash and duplicate skipping from CSV upload

Drop dedupeHash field and unique constraint from Transaction model.
Remove skipDuplicates from createMany. All rows in every upload are
now inserted unconditionally.

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

src/app/api/upload/route.ts

@@ -126,9 +126,7 @@ export async function POST(req: Request) {
         type: r.type,
         category: r.category ?? null,
         budgetId: r.budgetId,
-        dedupeHash: r.dedupeHash,
       })),
-      skipDuplicates: true,
     })
 
     const skippedCount = normalized.length - importedCount