Open first subpage when clicking Cookbook root entries

Add link to the first subpage on each Cookbook sidebar group (View,
Model, Message/Error, Browser Feature, RAP/EML, Expert Topic) so the
group header becomes navigable, matching the behavior of the entries
that already had a link.

Author: claude

docs/.vitepress/config.mjs

@@ -130,6 +130,7 @@ export default defineConfig({
           },
           {
             text: "View",
+            link: "/development/view/definition",
             collapsed: true,
             items: [
               { text: "Definition", link: "/development/view/definition" },
@@ -139,6 +140,7 @@ export default defineConfig({
           },
           {
             text: "Model",
+            link: "/development/model/binding",
             collapsed: true,
             items: [
               { text: "Binding", link: "/development/model/binding" },
@@ -173,6 +175,7 @@ export default defineConfig({
           },
           {
             text: "Message, Error",
+            link: "/development/messages/messages",
             collapsed: true,
             items: [
               { text: "Message", link: "/development/messages/messages" },
@@ -193,6 +196,7 @@ export default defineConfig({
           },
           {
             text: "Browser Feature",
+            link: "/development/specific/barcodes",
             collapsed: true,
             items: [
               {
@@ -218,6 +222,7 @@ export default defineConfig({
           },
           {
             text: "RAP, EML",
+            link: "/development/specific/cds",
             collapsed: true,
             items: [
               { text: "CDS", link: "/development/specific/cds" },
@@ -227,6 +232,7 @@ export default defineConfig({
           },
           {
             text: "Expert Topic",
+            link: "/development/specific/locks",
             collapsed: true,
             items: [
               { text: "Lock", link: "/development/specific/locks" },