fix(modules-12,14,15,18,19,25): editor note, refresh CI action pins, scaffold M15 merge

- M12: note the editor that `git revert -m 1 HEAD` opens (save/close, or --no-edit);
  the -m 1 / --no-ff merge teaching is unchanged.
- Refresh stale CI action pins to verified-current majors (actions/checkout @v4->@v7,
  actions/setup-python @v5->@v6; confirmed via GitHub Releases, 2026-06) across
  M14/M15/M18/M19/M25; add a Verify-before-publish item for pinned action versions.
- M15: scaffold the "slot security steps into the workflow" YAML merge (before/after
  diff, indentation caution, copy-whole-job alternative). Planted devices intact.

Closes #43
Closes #44
Closes #50

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

modules/12-revert-reset-and-recovery/README.md

@@ -296,6 +296,11 @@ do them once on purpose now.
    git log --oneline -3                      # you'll see a "Revert ..." commit on top
    ```
 
+   > `git revert` drops you into your text editor with a pre-filled "Revert …" message — save and
+   > close it (in vim, type `:wq` then Enter; in nano, Ctrl-O then Ctrl-X). Or add `--no-edit` to
+   > keep that default message and skip the editor entirely: `git revert -m 1 HEAD --no-edit`. Either
+   > way you end up with the same "Revert …" commit.
+
 7. Prove you're recovered — and notice nothing was erased:
 
    ```bash