applications: fix relative installer/link hrefs + serve /installers via IIS

Two problems with application download/launch/doc links:

1. Stored paths like 'installers/Foo.exe' are relative, so an <a href> on
   /shopdb/applications/6 resolved to /shopdb/applications/installers/Foo.exe.
   New basePath.fileHref() mounts a relative path under the app base
   (-> /shopdb/installers/Foo.exe) while leaving full URLs and UNC/file paths
   untouched. Applied to installpath, applicationlink, and documentationpath in
   the list and detail views.

2. Even the correct /shopdb/installers/Foo.exe 404s: httpPlatformHandler is
   path="*", so IIS forwards it to Flask, which has no such route. Add a
   web.config <location path="installers"> that clears the handler and serves
   that subpath as IIS static (with .exe/.msi MIME), from a physical
   APP_ROOT\installers folder.

plugins/applications/frontend/views/ApplicationDetail.vue

@@ -31,13 +31,13 @@
             <span v-if="app.ishidden" class="badge badge-lg badge-dark">Hidden</span>
           </div>
           <div class="hero-links" v-if="app.applicationlink || app.installpath || app.documentationpath">
-            <a v-if="app.applicationlink" :href="app.applicationlink" target="_blank" class="hero-link">
+            <a v-if="app.applicationlink" :href="fileHref(app.applicationlink)" target="_blank" class="hero-link">
               <span class="link-icon">&#x1F517;</span> Launch Application
             </a>
-            <a v-if="app.installpath" :href="app.installpath" target="_blank" class="hero-link">
+            <a v-if="app.installpath" :href="fileHref(app.installpath)" target="_blank" class="hero-link">
               <span class="link-icon">&#x2B07;</span> Download Files
             </a>
-            <a v-if="app.documentationpath" :href="app.documentationpath" target="_blank" class="hero-link">
+            <a v-if="app.documentationpath" :href="fileHref(app.documentationpath)" target="_blank" class="hero-link">
               <span class="link-icon">&#x1F4C4;</span> Documentation
             </a>
           </div>
@@ -167,6 +167,7 @@ import { useRoute } from 'vue-router'
 import { applicationsApi } from '@/api'
 import { getContactEmailDomain } from '@/utils/siteSettings'
 import { sanitizeNotesHtml } from '@/utils/sanitizeHtml'
+import { fileHref } from '@/utils/basePath'
 
 const route = useRoute()