feat: supplier name autocomplete on received invoices

- Added GET /api/admin/received-invoices/suppliers endpoint (distinct names)
- Upload and edit forms use HTML datalist for browser-native autocomplete
- Suggestions loaded once on page mount

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/admin/received-invoices.ts

@@ -87,6 +87,16 @@ export default async function receivedInvoicesRoutes(fastify: FastifyInstance):
     });
   });
 
+  // GET /api/admin/received-invoices/suppliers — distinct supplier names for autocomplete
+  fastify.get('/suppliers', { preHandler: requirePermission('invoices.view') }, async (_request, reply) => {
+    const results = await prisma.received_invoices.findMany({
+      select: { supplier_name: true },
+      distinct: ['supplier_name'],
+      orderBy: { supplier_name: 'asc' },
+    });
+    return success(reply, results.map(r => r.supplier_name));
+  });
+
   // GET /api/admin/received-invoices/:id/file
   fastify.get<{ Params: { id: string } }>('/:id/file', { preHandler: requirePermission('invoices.view') }, async (request, reply) => {
     const id = parseId(request.params.id, reply);