#164 Remove standalone page nav icons

Summary

• remove the frontmatter icons from Data and privacy and Domain migration so they render as text-only nav items
• add a regression test to keep those standalone pages from reintroducing sidebar icons

Tests

• node --test scripts/*.test.mjs
• node scripts/sweep-artifacts.mjs --check

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Summary by cubic

Removed the icon metadata from the Data and privacy and Domain migration pages so their sidebar nav items render as text-only. Added a regression test to ensure these pages stay icon-free.

• Bug Fixes
  • Removed icon from frontmatter on both pages to enforce text-only nav.
  • Added scripts/nav-frontmatter.test.mjs to assert no icon is set for these pages.