personal instance changes, potentially useful to main repo

[aminamos]

This PR refines chapter presentation, file naming, and content extraction in the audiobook conversion pipeline. NOTE: this was heavily vibecoded several months ago, if any changes are requested or required, I'll probably start over entirely.

autiobooks.py

• Chapter names in the UI now prefer display_name, with a fallback that humanizes raw filenames (underscore→space, title-case).
• Progress messages use real chapter names rather than numeric placeholders.
• Output WAV files adopt descriptive names (BookName_Introduction.wav), replacing the generic _chapter_1.wav pattern.
• Chapter names are sanitized to safe characters (alphanumeric, space, underscore, hyphen) and trimmed to 50 characters.

engine.py

• Introduces extract_chapter_content(), which preserves structural elements such as headings, lists, and special blocks.
• Headings are normalized using Markdown prefixes; lists use bullet markers; epigraphs are labeled explicitly.
• process_chapter() now unifies title extraction and content extraction.
• TOC and navigation files are more reliably detected and omitted.
• Faulty chapters are skipped safely via expanded try/except handling with error logging.