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/17-secrets-config-and-environments/lab/starter/.env.example

@@ -1,4 +1,4 @@
-# .env.example — the TEMPLATE you DO commit.
+# .env.example: the TEMPLATE you DO commit.
 #
 # This file documents which variables the app needs, with no real values. Teammates (and the
 # next AI session) copy it to a real `.env`, fill in the secrets, and never commit that copy.