Add numbered markers (S1, S2…) for cross-section positions on orthographic views

[dirlligafu]

Why this pull request?

This tool is a gem: free, accurate, local, and dead simple to use at a time when similar services charge way too much for watermarked, often inaccurate results. Cross-sections are one of its strongest features, especially for aircraft or any model where internal profile shapes matter. This small addition makes them easier to read when several cuts are used together.

What was added?

Currently, the dashed lines indicating cross-section positions on side and top views had no label, making it difficult to know which line corresponds to which section panel, especially with multiple cuts.

Changes:

• Each dashed line now shows a small S1, S2… marker, matching the existing SECTION 1, SECTION 2 caption style (same font, same alpha)
• A new checkbox "Number cross-section markers on views (S1, S2…)" controls the labels (unchecked by default)
• The checkbox is automatically disabled and unchecked when "Cross-section cut(s)" is off
• The preference is saved globally like all other settings

40 lines of code in 3 files, only additions, no deletion.

Preview:

Tested:

PNG and SVG output, with and without AO, up to 8 sections and on multiple color variations with no issue found

Side note:

Awesome tool you created there. Keep-up the good work, I can't wait for further enhancements you'll add!