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.

deploy/windows/web.config

@@ -76,4 +76,39 @@
     -->
 
   </system.webServer>
+
+  <!--
+    Installer downloads: serve /installers/* as IIS static files instead of
+    forwarding them to Flask. The handler above is path="*", so without this a
+    request for /installers/Foo.exe goes to waitress, which has no such route
+    (SPA fallback), and large binaries would stream through a Python thread.
+
+    This <location> clears the httpPlatformHandler for that one subpath and puts
+    the static file handler back, so IIS serves the bytes directly (kernel-mode,
+    range/resume, no Python thread held).
+
+    Requires a physical folder at APP_ROOT\installers (the site's physical path
+    is APP_ROOT). Drop the installer binaries there, e.g. robocopy them from the
+    classic wwwroot\installers. The stored installpath 'installers/Foo.exe' then
+    resolves to <mount>/installers/Foo.exe (e.g. /shopdb/installers/Foo.exe).
+
+    .exe/.msi are given an explicit MIME map; if the parent site has a Request
+    Filtering rule that denies executable extensions, also allow them there.
+  -->
+  <location path="installers">
+    <system.webServer>
+      <handlers>
+        <clear />
+        <add name="StaticFile" path="*" verb="*"
+             modules="StaticFileModule" resourceType="File"
+             requireAccess="Read" />
+      </handlers>
+      <staticContent>
+        <remove fileExtension=".exe" />
+        <mimeMap fileExtension=".exe" mimeType="application/octet-stream" />
+        <remove fileExtension=".msi" />
+        <mimeMap fileExtension=".msi" mimeType="application/octet-stream" />
+      </staticContent>
+    </system.webServer>
+  </location>
 </configuration>