docs(slack): swap demo video and add model choice to Capabilities

docs/integrations/slack.mdx

@@ -63,7 +63,7 @@ With the Slack integration, you can:
 
 <Frame caption="Factory Slack integration demo">
   <video controls preload="metadata">
-    <source src="/images/marketing/slack-demo.mp4" type="video/mp4" />
+    <source src="/images/marketing/slack-clone-scene.mp4" type="video/mp4" />
   </video>
 </Frame>
 
@@ -73,8 +73,14 @@ With the Slack integration, you can:
 - Include supported image attachments from Slack as session context
 - Have Droid post messages, generated files, artifacts, and result videos back to Slack
 - Send follow-up messages and attachments from Slack into an active Droid session
+- **Use any model you want, no lock-in.** Factory is model-agnostic: choose Claude, GPT, Gemini, open-source/Droid Core, or any of 30+ supported models
+- Pick the model when you start a session, set a default **model** per channel for Auto-Run and service-account workflows, or let [Factory Router](/web/factory-router) pick the best model automatically
 - Reference Slack threads in Factory by pasting a thread URL into a Factory chat
 
+<Frame caption="Pick a specific model, or let Factory Router choose automatically, for a Slack-started session">
+  <img src="/images/slack-model-selection.png" alt="Factory Session Settings dialog showing the model picker with Factory models" />
+</Frame>
+
 When creating a PR, the Slack integration will also use a subagent to handle CI so the agent can respond faster.
 
 When a Slack thread is imported, Factory has access to the entire conversation history, allowing it to provide context-aware assistance.