docs: replace em dashes with plain punctuation across prose

Swap em dashes for commas/colons/periods in the README, skills, AGENTS.md and
its five rule copies, examples, command files, and benchmark README. Rule
copies stay in sync (same edit applied to all) and the invariant guard passes.

Left untouched on purpose: the vendored caveman SKILL.md (verbatim third-party
text), the dated benchmark writeups in results/ (historical records), and
.js code comments.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

examples/api-endpoint.md

@@ -46,7 +46,7 @@ def get_user(user_id: int, service: UserService = Depends(get_user_service)):
         raise HTTPException(status_code=404, detail="User not found")
 ```
 
-Five files, three classes, a custom exception, and a dependency-injection chain — wrapping one database call.
+Five files, three classes, a custom exception, and a dependency-injection chain, wrapping one database call.
 
 ## With Ponytail