feat(docs-site): redirect ktx.sh/slack to Slack community invite (#224)

Add a host-scoped redirect for /slack on ktx.sh before the existing
catch-all so the path resolves to the community invite link instead of
docs.kaelio.com/ktx/slack.

docs-site/next.config.mjs

@@ -34,6 +34,14 @@ const config = {
         permanent: true,
         basePath: false,
       },
+      {
+        source: "/slack",
+        has: [{ type: "host", value: "ktx.sh" }],
+        destination:
+          "https://join.slack.com/t/ktxcommunity/shared_invite/zt-3y9b44m1x-LVyNNJD5nwaZHq4XS29LMQ",
+        permanent: false,
+        basePath: false,
+      },
       {
         source: "/:path*",
         has: [{ type: "host", value: "ktx.sh" }],