style(no-slop): remove every em-dash + banned words across all modules + capstone

Apply the no-ai-slop standard (now binding in AGENTS.md): the em-dash character is
banned outright (restructured, not blind-replaced), plus the banned word/phrase
list (delve, leverage, robust, seamless, truly, unlock, etc.). 0 em-dashes remain
in modules + capstone; the only "robust" left is the planted M10 ai-change.patch
trap. Module H1 titles use a colon separator.

All deliberate teaching devices preserved; labs compile/parse (py/sh/yaml/json);
no junk. AGENTS.md updated with the hard no-slop rules.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TfzV5QvtPDz8LJS3Pu5VLT

modules/13-testing-in-the-ai-era/lab/tasks-app/tasks.py

@@ -2,7 +2,7 @@
 
 Same running example from Modules 1 and 2, carried forward. It has grown one feature since then:
 a `pending_count()` helper that the AI added to back a `count` command. The feature "works" in
-the obvious case — which is exactly the kind of code this module teaches you to verify properly.
+the obvious case, which is exactly the kind of code this module teaches you to verify properly.
 """
 
 from dataclasses import dataclass, field