Fix HtmlToDjot table and reference escaping

[dereuromark]

Summary

• escape literal pipes in serialized table cells so single-cell content cannot split rows
• fall back from unsafe reference-style links and images to inline syntax instead of emitting broken labels
• strip internal data-djot-* markers from raw HTML inline fallbacks

Testing

• vendor/bin/phpunit tests/TestCase/Converter/HtmlToDjotTest.php
• vendor/bin/phpunit tests/TestCase/Converter/HtmlToDjotTest.php tests/TestCase/RoundTripTest.php tests/TestCase/DjotConverterTest.php tests/TestCase/ProfileTest.php
• vendor/bin/phpstan analyse src --no-progress
• composer cs-check
• vendor/bin/phpunit

[codecov]

Codecov Report

❌ Patch coverage is 76.47059% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.61%. Comparing base (e17f382) to head (906d65f).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Converter/HtmlToDjot.php	76.47%	8 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #175      +/-   ##
============================================
- Coverage     93.68%   93.61%   -0.08%     
- Complexity     3220     3241      +21     
============================================
  Files            93       93              
  Lines          8171     8203      +32     
============================================
+ Hits           7655     7679      +24     
- Misses          516      524       +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.