v2.1.2 - Bold slide counters and README refresh

Slide counters

• Rendered the top-right progress frame number with \bfseries, matching the
  black bold face used by slide titles and emphasized text when
  Rounded-X Mgen+ 1cp is available.
• Kept the progress-circle layout unchanged while making the displayed number
  visually consistent across the Japanese and English templates.

Table of contents

• Applied the same bold face to projected section numbers in automatic
  table-of-contents slides.
• Preserved the existing projected-number size so the circular markers keep
  their original fit.

README

• Updated the README description to mention the bold progress and section
  numbers.
• Regenerated the README screenshots from the updated PDFs at 300 dpi.
• Added the English title and contents screenshots to the README preview block
  so the updated section-number markers are visible in the documentation.

Compatibility

This is a patch release. No macro names or slide-source changes are required
for existing decks.