feat:계약일 date input 입력 가능하게 변경

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

app/Http/Controllers/Sales/AdminProspectController.php

@@ -323,6 +323,30 @@ public function updateHqStatus(int $id, Request $request)
         ]);
     }
 
+    /**
+     * 계약일 변경
+     */
+    public function updateContractedDate(int $id, Request $request)
+    {
+        $this->checkAdminAccess();
+
+        $request->validate([
+            'contracted_at' => 'nullable|date',
+        ]);
+
+        $prospect = TenantProspect::findOrFail($id);
+        $management = SalesTenantManagement::findOrCreateByProspect($prospect->id);
+
+        $management->update([
+            'contracted_at' => $request->input('contracted_at') ?: null,
+        ]);
+
+        return response()->json([
+            'success' => true,
+            'contracted_at' => $management->contracted_at?->format('Y-m-d'),
+        ]);
+    }
+
     /**
      * 인계일 수동 변경
      */