Build out all 27 modules + capstone (#1)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

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

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+# Demo app — `tasks` (Module 13 copy)
+
+The same tiny task tracker from Modules 1 and 2, with one feature added: a `count` command backed
+by `TaskList.pending_count()`. Use this copy for the Module 13 lab so everyone starts from the same
+code — including the same latent bug.
+
+If you already have a `tasks-app` from earlier modules, you can use that instead; just make sure it
+has a `count` command (the Module 2 lab added one). The planted bug in this copy is there on purpose.
+
+## Files
+
+- `tasks.py` — core logic (`Task`, `TaskList`), now with `pending_count()`.
+- `cli.py` — command-line front end. Adds `count`.
+
+## Run it
+
+```bash
+python cli.py add "write the tests"
+python cli.py add "fix the bug"
+python cli.py done 0
+python cli.py list
+python cli.py count
+```
+
+Requires Python 3.10+. No third-party packages — tests use the standard library `unittest`.