fix(template): import beta plugins from /beta subpath

The init template hard-coded a single `from '@databricks/appkit'` import
for every plugin, which would resolve to `undefined` for beta plugins
(they live behind the `/beta` subpath export).

Splits the import emission by plugin stability:
- Stable plugins stay on the existing line.
- Each beta plugin gets its own `from '@databricks/appkit/beta'`
  import line.

Backwards-compatible with the current Databricks CLI: until pluginVar
exposes Stability, `$p.Stability` resolves to the empty string, every
plugin compares unequal to "beta", and rendering matches today's
output. Once databricks/cli#5090 lands the field, beta plugins start
routing to the right import automatically.

The plugins: [...] array body is unchanged — both stable and beta
plugins are constructed identically (`plugin()`) once they're in
scope, so the runtime call list doesn't depend on tier.

Signed-off-by: MarioCadenas <MarioCadenas@users.noreply.github.com>

Author: MarioCadenas

template/server/server.ts

@@ -1,4 +1,9 @@
-import { createApp{{range $name, $_ := .plugins}}, {{$name}}{{end}} } from '@databricks/appkit';
+import { createApp{{range $name, $p := .plugins}}{{if ne $p.Stability "beta"}}, {{$name}}{{end}}{{end}} } from '@databricks/appkit';
+{{- range $name, $p := .plugins}}
+{{- if eq $p.Stability "beta"}}
+import { {{$name}} } from '@databricks/appkit/beta';
+{{- end}}
+{{- end}}
 {{- if .plugins.lakebase}}
 import { setupSampleLakebaseRoutes } from './routes/lakebase/todo-routes';
 {{- end}}