test(docs): add command-count sync test; fix ARCHITECTURE.md drift (#2257) (#2259)

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>

docs/ARCHITECTURE.md

@@ -113,7 +113,7 @@ User-facing entry points. Each file contains YAML frontmatter (name, description
 - **Copilot:** Slash commands (`/gsd-command-name`)
 - **Antigravity:** Skills
 
-**Total commands:** 69
+**Total commands:** 73
 
 ### Workflows (`get-shit-done/workflows/*.md`)
 
@@ -409,7 +409,7 @@ UI-SPEC.md (per phase) ───────────────────
 
 ```
 ~/.claude/                          # Claude Code (global install)
-├── commands/gsd/*.md               # 69 slash commands
+├── commands/gsd/*.md               # 73 slash commands
 ├── get-shit-done/
 │   ├── bin/gsd-tools.cjs           # CLI utility
 │   ├── bin/lib/*.cjs               # 19 domain modules