docs: turn the version banners into working cross-site links (#2396)

Author: felixweinberger

docs/.vitepress/theme/Banner.vue

@@ -1,6 +1,5 @@
 <template>
     <div class="version-banner">
-        You are viewing the in-development v2 documentation. The stable v1 docs are at
-        <a href="https://ts.sdk.modelcontextprotocol.io/">ts.sdk.modelcontextprotocol.io</a>.
+        Looking for the <a href="https://ts.sdk.modelcontextprotocol.io/" target="_self">v1 documentation</a>?
     </div>
 </template>

docs/v1/.vitepress/theme/Banner.vue

@@ -1,6 +1,5 @@
 <template>
     <div class="version-banner">
-        You are viewing the v1.x documentation. The in-development v2 docs are at
-        <a href="https://ts.sdk.modelcontextprotocol.io/v2/">/v2/</a>.
+        Looking for the <a href="https://ts.sdk.modelcontextprotocol.io/v2/" target="_self">v2 beta documentation</a>?
     </div>
 </template>