Rework PDF export: book typography, theme colors, own markdown renderer

[Wavesonics]

Summary

Replaces the pdfkmp-markdown module with our own markdown renderer (PdfProseMarkdown.kt) built on the same intellij-markdown engine the EPUB export uses (GFM flavour), giving the PDF export book typography that pdfkmp's markdown module could not express:

• First-line paragraph indents on every paragraph, with no blank line between consecutive paragraphs — the indent is the separator. Rendered as a run of NBSPs since pdfkmp's layout engine has no indent primitive (swap for a real firstLineIndent if upstream grows one).
• Roomier line spacing: 1.5x leading on body text, 1.25x on headings, plus dedicated gaps under chapter titles and in-chapter headings.
• Project theme colors, mirroring the EPUB stylesheet: primary on the title page (with accent rule), contents, chapter headings, h1s, and links; secondary on h2s.

Also fixes for free, by virtue of the spec-compliant parser: backslash-escape handling (the stripBackslashEscapes workaround is gone) and PDF/EPUB now parse markdown with the same engine so the two exports cannot disagree on structure.

Testing

• 17 new unit tests for the AST walker (PdfProseMarkdownTest), plus the existing export integration tests.
• PdfProseVisualCheck (env-gated, skipped in CI) renders a sample PDF for eyeballing typography changes; output verified visually.

🤖 Generated with Claude Code

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 143 complexity · 0 duplication

Metric	Results
Complexity	143
Duplication	0

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[codecov]

Codecov Report

❌ Patch coverage is 54.84848% with 149 lines in your changes missing coverage. Please review.
✅ Project coverage is 52.84%. Comparing base (0791954) to head (c058084).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #585      +/-   ##
===========================================
+ Coverage    52.78%   52.84%   +0.05%     
===========================================
  Files          440      441       +1     
  Lines        18491    18803     +312     
  Branches      2679     2794     +115     
===========================================
+ Hits          9761     9936     +175     
- Misses        7954     8041      +87     
- Partials       776      826      +50     

Components	Coverage Δ
Client	53.98% <54.84%> (+0.05%)	⬆️
Server	50.70% <ø> (ø)

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