Fix TabsExtension breaking TableOfContentsExtension

[dereuromark]

Summary

Fixes #139

The TabsExtension was calling $converter->render() for nested tab content, which triggered clear() on all extensions including TableOfContentsExtension. This wiped out all headings collected before the tabs div, causing TOC to only show headings that appeared after the tabs.

Root Cause

In DjotConverter::render():

public function render(Document $document): string
{
    foreach ($this->extensions as $extension) {
        if (method_exists($extension, 'clear')) {
            $extension->clear();
        }
    }
    return $this->renderer->render($document);
}

When TabsExtension called $converter->render($tempDoc) to render tab panel content, it triggered this clear() which reset the TOC's $this->toc = [].

Fix

Use the renderer directly via $converter->getRenderer()->render() instead of $converter->render() to avoid triggering the clear() call on extensions.

Changes

• Modified TabsExtension to use renderer directly for nested content
• Added 3 regression tests for TOC compatibility:
  • testCompatibilityWithTableOfContents - verifies all headings before/after tabs are captured
  • testTocCapturesHeadingsInsideTabs - verifies H2s around tabs are captured
  • testTocWithTabsUsingLabelAttribute - verifies headings inside tabs with label attribute are captured

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.21%. Comparing base (46d5866) to head (d42caee).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #140   +/-   ##
=========================================
  Coverage     94.21%   94.21%           
  Complexity     2570     2570           
=========================================
  Files            88       88           
  Lines          6846     6847    +1     
=========================================
+ Hits           6450     6451    +1     
  Misses          396      396           

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