Link the models guide with a validated liquid tag

The /guides/models/ URL 404s: jekyll-redirect-from emits flat
guides/models.html files, which GitHub Pages serves without a
trailing slash but not with one. Use {% link _advanced/models.md %}
instead, which resolves to the canonical /models/ URL at build time
and fails the build if the target moves. The tag targets the 1.x
docs tree because the generated page only renders in the frozen 1.x
site build; the /next build replaces it with a redirect stub.

Author: crmne

docs/_reference/available-models.md

@@ -29,7 +29,7 @@ Your installed gem may bundle an older snapshot of the registry. Refresh it to g
 RubyLLM.models.refresh!
 ```
 
-See [the models guide](https://rubyllm.com/guides/models/) for how refreshing works in plain Ruby and Rails.
+See [the models guide]({% link _advanced/models.md %}) for how refreshing works in plain Ruby and Rails.
 
 ## Models by Provider
 

tasks/models.rake

@@ -157,6 +157,9 @@ def status(provider_sym)
   end
 end
 
+# The generated page renders inside the frozen 1.x site build; the /next
+# build replaces it with a redirect stub (docs/bin/build-versions.sh).
+# Liquid links must therefore target the 1.x docs tree.
 def generate_models_markdown
   models = RubyLLM.models.all
   total_models = models.count
@@ -195,7 +198,7 @@ def generate_models_markdown
     RubyLLM.models.refresh!
     ```
 
-    See [the models guide](https://rubyllm.com/guides/models/) for how refreshing works in plain Ruby and Rails.
+    See [the models guide]({% link _advanced/models.md %}) for how refreshing works in plain Ruby and Rails.
 
     ## Models by Provider