fix: respect custom filename during PDF generation

[Jannik-cmyk]

Summary

• use outFilename as the source HTML file during PDF generation
• derive the PDF filename from the configured HTML filename
• construct cross-platform-safe file URLs
• always close Puppeteer after success or failure
• add focused regression tests for default, custom and failing paths

Root cause

The HTML template writes the generated documentation to
params.outFilename || 'index.html', but the PDF hook always read
index.html and wrote index.pdf. PDF generation therefore failed or
generated the wrong output whenever outFilename was customized.

Validation

• node --check hooks/99_generatePdf.js
• node --check test/hooks/99_generatePdf.test.js
• direct mocked Node harness covering filename derivation, URL encoding,
  browser cleanup and failure paths
• git diff --check
• npm run lint

The repository Jest and generator suites could not be executed locally because
the required dependencies and CLI were unavailable in the execution
environment. They will be validated by the repository CI.

Fixes #826

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud