Return 405 on GET /mcp so idle SSE streams stop exhausting Cloud Run - #4181

Changed pages include:

• index.html - view
• 404.html - view
• ai-docs-security/index.html - view
• chainguard/index.html - view
• compliance/index.html - view
• contributors/index.html - view
• developer-resources/index.html - view
• get-started/index.html - view
• guidelines/index.html - view
• mcp-server-ai-docs/index.html - view

There are more changes not included in the list