fix(running-example): consistent lab-script paths, tasks.json policy, no command collisions

- Lab-script path convention: course scripts live in modules/NN/lab/; copy the
  one a step needs into tasks-app, then run by bare name (M4/M6/M7/M26 + headers).
- tasks.json stays gitignored: M20 verifies via `cli.py list`/`cat tasks.json`
  (not git diff) and frames runtime state as deliberately ignored; M22 cleanup
  uses `rm tasks.json`; M10 review-lab gets its own .gitignore.
  Module 21's lab deliberately ships NO .gitignore (teaching device) — untouched.
- Stop running-example command collisions: M5 clear->search, M6 count/clear->
  stats/purge, M7 clear/count->wipe/remaining (README + scripts + agent prompts +
  branch/worktree names). M6 conflict still reproduces on the carried usage line.

Closes #7
Closes #10
Closes #11

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

modules/06-branches-sandboxes-for-experiments/lab/make-conflict.sh

@@ -9,8 +9,9 @@
 # read the <<<<<<< / ======= / >>>>>>> markers, edit to the version you want, remove the markers,
 # then `git add` + `git commit`.
 #
-# Run it from anywhere inside your tasks-app repo:
-#     bash modules/06-branches-sandboxes-for-experiments/lab/make-conflict.sh
+# Copy it into your tasks-app repo, then run it from inside the repo:
+#     cp /path/to/modules/06-branches-sandboxes-for-experiments/lab/make-conflict.sh .
+#     bash make-conflict.sh
 #
 # It is non-destructive to your real work: it only touches README.md on two throwaway practice
 # branches and refuses to run if your working tree is dirty.