Remove Copilot documentation and redirect to Neo product page (#16439)

Removes the standalone Copilot article from the AI documentation section
and redirects all Copilot URLs to the Neo product page. Copilot has been
superseded by Neo, so the documentation should point users to the current
product.

Changes:
- Removed /docs/ai/copilot/_index.md and associated images
- Added copilot URL aliases to /product/neo.md to redirect to Neo
- Removed copilot aliases from /docs/ai/_index.md
- This removes "Copilot" from the Infrastructure AI sidebar menu

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: arturl

content/docs/ai/_index.md

@@ -14,10 +14,6 @@ aliases:
 - /docs/iac/neo/
 - /docs/neo/
 - /docs/ai/neo/
-- /docs/ai/copilot/
-- /docs/pulumi-cloud/copilot/
-- /docs/intro/copilot/
-- /docs/intro/pulumi-cloud/copilot/
 menu:
     ai:
         identifier: ai-home

content/docs/ai/copilot/_index.md

@@ -1,7 +1,7 @@
 ---
 title: "Pulumi Neo - Your AI Platform Engineer"
 layout: neo
-aliases: ["/neo", "/copilot", "/product/copilot", "/product/pulumi-copilot"]
+aliases: ["/neo", "/copilot", "/product/copilot", "/product/pulumi-copilot", "/docs/ai/copilot/", "/docs/pulumi-cloud/copilot/", "/docs/intro/copilot/", "/docs/intro/pulumi-cloud/copilot/"]
 
 heading: Pulumi Neo
 subheading: |