Add tests/command-count-sync.test.cjs which programmatically counts
.md files in commands/gsd/ and compares against the two count
occurrences in docs/ARCHITECTURE.md ("Total commands: N" prose line and
"# N slash commands" directory-tree comment). Counts are extracted from
the doc at runtime — never hardcoded — so future drift is caught
immediately in CI regardless of whether the doc or the filesystem moves.
Fix the current drift: ARCHITECTURE.md said 69 commands; the actual
committed count is 73. Both occurrences updated.
Closes#2257
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
