Support subpath IIS deployment as a second install method

The app can run as an IIS Application under an existing site
(e.g. https://host/ops/) instead of its own site + port:

- frontend: vite base via VITE_BASE_PATH; router history, axios
  baseURL, and root-absolute asset/route paths resolve through
  utils/basePath.js withBase()
- backend: MOUNT_PATH (env or .env) wraps the app in a WSGI
  middleware that shifts the prefix into SCRIPT_NAME, so one knob
  serves API + SPA under the mount
- docs: INSTALL-WINDOWS-IIS.md section 7b runbook + troubleshooting
  rows; DEPLOY-WINDOWS-IIS.md pointer; commented examples in
  deploy/windows/web.config and .env.example

Root deployment unchanged (MOUNT_PATH unset, base '/'). Also folds
two stray root-absolute callers into the shared plumbing
(MachineForm relationship-types fetch, reports CSV window.open).

frontend/src/views/machines/MachineForm.vue

@@ -347,7 +347,7 @@
 <script setup>
 import { ref, onMounted, computed, watch } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
-import { machinesApi, vendorsApi, locationsApi, modelsApi, businessunitsApi, computersApi, assetsApi } from '../../api'
+import { machinesApi, vendorsApi, locationsApi, modelsApi, businessunitsApi, computersApi, assetsApi, relationshipTypesApi } from '../../api'
 import ShopFloorMap from '../../components/ShopFloorMap.vue'
 import Modal from '../../components/Modal.vue'
 import CustomFieldsInputs from '../../components/CustomFieldsInputs.vue'
@@ -463,11 +463,8 @@ onMounted(async () => {
 
     // Load relationship types separately
     try {
-      const relRes = await fetch('/api/assets/relationshiptypes')
-      if (relRes.ok) {
-        const relData = await relRes.json()
-        relationshipTypes.value = relData.data || []
-      }
+      const relRes = await relationshipTypesApi.list()
+      relationshipTypes.value = relRes.data.data || []
     } catch (e) {
       // Fallback - use hardcoded Controls type
       relationshipTypes.value = [{ relationshiptypeid: 1, relationshiptype: 'Controls' }]