fix(modules-4,7,14): make the git demos/labs actually do what the prose claims

- M4 Part C now commits the reviewed `delete` change as the checkpoint, so
  Part D's `git restore .` returns to a delete-containing state (was wiping it).
- M7 'watch it break': switch to an existing divergent branch so the
  "would be overwritten by checkout" refusal actually fires (git switch -c never did).
- M7 Part C: demonstrate worktree isolation with existing add/list and distinct
  per-worktree data; move the new clear/count commands to after they exist.
- M14 Part C: recover with `git revert HEAD` (Module 12, which precedes M14) so
  CI legitimately goes green; drop the wrong "Module 2's safety net" attribution.

Closes #2
Closes #3
Closes #4
Closes #12

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

modules/14-continuous-integration/README.md

@@ -274,15 +274,21 @@ and watch CI stop it.
    `test_pending_excludes_completed_tasks` failed, with the assertion and the actual-vs-expected
    values. CI caught in seconds what a skim would have waved through.
 
-9. Reproduce and fix:
+9. Reproduce and fix. The bad change is already committed *and pushed*, so `git restore` is no help
+   here — it only discards *uncommitted* edits, and there are none. The team-safe undo for something
+   already on shared history is `git revert` (Module 12): it writes a **new** commit that inverts the
+   bad one, instead of rewriting history other people may have pulled.
 
    ```bash
    pytest -q          # fails locally too — same command, same failure
-   git restore tasks.py   # throw away the bad change (Module 2's safety net)
-   git commit -am "Revert: pending() must exclude completed tasks"
-   git push           # CI goes green again
+   git revert HEAD    # new commit that undoes "Simplify pending()" (Module 12)
+   git push           # CI re-runs on the fixed code and goes green again
    ```
 
+   `git revert HEAD` opens an editor with a prefilled message (`Revert "Simplify pending()"`) — save
+   and close it. The revert restores the correct `pending()`, the push triggers CI on the fixed code,
+   and the run goes green.
+
 10. *(Optional, to feel the linter tier.)* Add an obviously unused import to `cli.py`
     (`import os` at the top, unused), commit, and push. Watch the **Lint** step fail *before* the
     tests even run — the cheap check failing fast. Remove it and push again.