[BUG] Pagination algorithm causes content overflow in reader mode

[DeepanshKhurana]

Bug Report

Describe the bug
The pagination algorithm uses line-based estimation that compounds errors across content blocks. Content frequently overflows the column height or gets cut off mid-sentence.

To Reproduce

1. Create a piece with mixed content (paragraphs, blockquotes, lists)
2. Open in reader mode with 2-column layout
3. Observe content being cut off at column boundaries or overflowing

Expected behavior
Content should fit within column boundaries without overflow or cutoff.

Screenshots
N/A

Additional context
The line-based approach estimates lines per block using character counts divided by average characters per line, but this compounds errors because:

• Markdown formatting (bold, italic) affects rendered width unpredictably
• Blockquotes and lists have different effective widths
• Per-sentence line buffers add cumulative overhead
• No mechanism to split blocks mid-content when they exceed remaining space