Rewrite setup and teardown scripts documentation

[sbezludny]

Summary

• Full rewrite of the main setup and teardown scripts reference page with expanded content
• Renamed file from set-up-and-tear-down.mdx to setup-and-teardown.mdx for consistency
• Added permanent redirect from old URL to new URL
• Updated guide page with teardown coverage and combined patterns

Key improvements

• Fixed page title from "Set Up and Tear Down" to "Setup and Teardown"
• Added execution flow diagram (Mermaid) showing script lifecycle
• Expanded teardown section with response modification and cleanup examples
• Documented error handling differences (setup aborts check, teardown continues)
• Added "Modifiable" column to request/response tables
• Removed broken link to non-existent teardown examples page
• Updated 12 files with internal links to new path

Test plan

• Run mintlify dev and verify pages render correctly
• Check Mermaid diagram renders properly
• Verify internal links resolve
• Test redirect works after deployment

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