move display math punctuation inside formula blocks

Move trailing punctuation (periods, commas) from outside display math
closing `$` to inside the formula content, e.g. `$.\n` → content line
gets `.` appended and closing becomes `$\n`. Affects 100 instances
across both multi-line and single-line display equations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: isPANN