docs(gif): bump FontSize 17 -> 15 to fit wider CLASS-column table

[cicdteam]

Summary

PR #19 added a CLASS column to the scan table, growing its width from ~102 chars to ~122 chars. At FontSize 17 with the canvas at 1280x760, the wider table was borderline / wrapping in the GIF.

Drop FontSize 17 -> 15 (~12% smaller, still ~15% bigger than the original 13 we shipped before). This gives the table ~20 cols of buffer at 1280px width and the box-drawing characters render cleanly across all three frames.

GIF size 601 KB -> 522 KB.

Test plan

• Regenerated locally against demo stack.
• All three frames (first scan, --ignore demo, JSON output) visually checked - table renders with intact box-drawing, content fits with margin.
• CI green.