docs: add ABAP Cloud, BTP group; promote Installation

Move the Installation page to the top of the Configuration sidebar as
an independent entry. Replace the former Installation parent group with
a new 'ABAP Cloud, BTP' group containing S/4 Public Cloud, BTP ABAP Env,
Build Work Zone, and Mobile Start. Add stub pages for BTP ABAP Env and
Mobile Start.

Author: claude

docs/.vitepress/config.mjs

@@ -185,6 +185,7 @@ export default defineConfig({
         link: "/configuration/setup",
         collapsed: true,
         items: [
+          { text: "Installation", link: "/configuration/installation" },
           { text: "General", link: "/configuration/setup" },
           { text: "Security", link: "/configuration/security" },
           { text: "Authorization", link: "/configuration/authorization" },
@@ -195,14 +196,15 @@ export default defineConfig({
           { text: "Debugging", link: "/configuration/troubleshooting" },
           { text: "Fiori Launchpad", link: "/configuration/launchpad" },
           {
-            text: "Installation",
-            link: "/configuration/installation",
+            text: "ABAP Cloud, BTP",
             items: [
               {
                 text: "S/4 Public Cloud",
                 link: "/configuration/s4_public_cloud",
               },
-              { text: "BTP Work Zone", link: "/configuration/btp" },
+              { text: "BTP ABAP Env", link: "/configuration/btp_abap_env" },
+              { text: "Build Work Zone", link: "/configuration/btp" },
+              { text: "Mobile Start", link: "/configuration/mobile_start" },
             ],
           },
         ],

docs/configuration/btp_abap_env.md

@@ -0,0 +1,6 @@
+---
+outline: [2, 4]
+---
+# BTP ABAP Environment
+
+The setup in `BTP ABAP Environment` matches `S/4 Public Cloud`. Follow the [S/4 Public Cloud](/configuration/s4_public_cloud) guide.

docs/configuration/mobile_start.md

@@ -0,0 +1,6 @@
+---
+outline: [2, 4]
+---
+# Mobile Start
+
+Embed your abap2UI5 apps into SAP Mobile Start. See [**Setup SAP Mobile Start**](https://www.linkedin.com/pulse/abap2ui5-integration-sap-business-technology-platform-33-setup-uzure/) for details.