Add Connect account deletion page

[callumalpass]

Summary

• add a public /account-deletion/ page with exact mdbase Connect deletion steps for TaskNotes users
• document deleted data, local and audit data that may remain, and background hosted cleanup behavior
• link the page from the site footer and style numbered legal-page steps consistently

Validation

• MDBASE_SPEC_DIR=/home/calluma/projects/mdbase-spec pnpm test
  • deployment script tests passed
  • Connect release record verified
  • Astro check: 0 errors, warnings, or hints
  • production build generated /account-deletion/
  • imported specification and checked 30 HTML files with no broken local links
• inspected built HTML for the page title, account-settings URL, TaskNotes wording, deleted and retained data, non-fixed retention language, background cleanup wording, and footer link