docs: add interactive Markdown examples

[rdlabo]

Summary

• make docs/special-markup.md the canonical source for the demo docs page
• generate syntax-highlighted HTML with Marked and Shiki
• render live Ionic examples from the same markup as each code sample
• document and demonstrate iOS26 opt-ins, including a scrollable condense-header search example

Verification

• npm test -- --watch=false
• npm run lint
• npm run build
• visual checks in iOS mode at mobile and wide viewports

[github-actions]

Playwright test results

 90 passed

Details

 90 tests across 2 suites
 1 minute, 50 seconds
 498d438
 This detailed result covers Ionic 9 only. Ionic 8 runs against the same screenshots in a separate matrix job; check the workflow run for both results. To update the screenshots, comment with /update-screenshots.

[github-actions]

📊 Ionic 9 Playwright Test Report

View the detailed Ionic 9 report: https://rdlabo-dev.github.io/ionic-theme-ios26/pr-118/

Ionic 8 runs against the same screenshots in a separate matrix job. View both results in the workflow run.