fix: add numpy install sections to L1-L4 answers, close TODO, tweak AGENTS.md

- Add the missing "Package installation" section (%%capture %pip install
  numpy) to L1, L2, L3 and L4 exercise answers, matching the L5 and
  tutorial lessons
- TODO.md: mark the text-based notebooks section as achieved in August
  2026 (classic .ipynb notebooks migrated to MyST text notebooks in
  PR #9) and cross out the completed items
- AGENTS.md: fix the "files excluded from version control" section,
  which claimed venv/ and _build/ were git-ignored although no root
  .gitignore exists

Co-authored-by: openhands <openhands@all-hands.dev>

Author: openhands-agent

AGENTS.md

@@ -176,9 +176,10 @@ Thank you! Please report it at https://github.com/MarinhoLab/OpenExecutableBooks
 - Example: `fix/typos-and-uk-english`, `feat/add-lesson6`
 
 ### Files excluded from version control:
-- `venv/` — Python virtual environment
-- `_build/` — Build artifacts
-- `basic_lessons/*.ipynb` — Generated at build time from `.md` files
+- `basic_lessons/*.ipynb` — Generated at build time from `.md` files (via `basic_lessons/.gitignore`)
+
+There is intentionally no root `.gitignore`. If you create local `venv/` or `_build/`
+directories, keep them out of commits (e.g. via `.git/info/exclude`).
 
 ---
 

TODO.md

@@ -11,14 +11,19 @@ that properly shows the video but not the image.
 
 ## Text-based notebooks
 
-- Converting from traditional Jupyter notebooks to text-based notebooks might be an interesting topic to explore. See
+**Done — achieved in August 2026.** The lessons were migrated from classic Jupyter
+notebooks to MyST text-based notebooks (`.md` with `{code-cell}` directives), stored
+under `basic_lessons/` (see [PR #9](https://github.com/MarinhoLab/OpenExecutableBooksRobotics/pull/9)).
+The items below are therefore no longer open:
+
+- ~~Converting from traditional Jupyter notebooks to text-based notebooks might be an interesting topic to explore. See
   [link](https://myst-nb.readthedocs.io/en/latest/authoring/text-notebooks.html#authoring-text-notebooks). Classic notebooks
   store cell output on themselves, with implications on version control software. While classic Jupyter notebooks are more
-  easily usable without extensions, `jupytext` seemingly allows for the conversions. See [link](https://jupyterbook.org/en/stable/file-types/myst-notebooks.html).
-- The so-called [paired notebooks](https://jupytext.readthedocs.io/en/latest/paired-notebooks.html) are possibly the solution. 
+  easily usable without extensions, `jupytext` seemingly allows for the conversions. See [link](https://jupyterbook.org/en/stable/file-types/myst-notebooks.html).~~
+- ~~The so-called [paired notebooks](https://jupytext.readthedocs.io/en/latest/paired-notebooks.html) are possibly the solution. 
   Given that the latex macros sometimes do not render well in `jupyterlab`, this could become indirectly a solution.
   The latex support for `myst` is much less hacky, so it is likely that the notebooks exported from the text version
-  are more likely to be compatible with `jupyterlab`.
+  are more likely to be compatible with `jupyterlab`.~~
 
 ## Notes
 

basic_lessons/lesson1_exercise_answers.md

@@ -13,6 +13,12 @@ kernelspec:
 ## I found an issue
 Thank you! Please report it at https://github.com/MarinhoLab/OpenExecutableBooksRobotics/issues
 
+# Package installation
+
+````{code-cell}
+%%capture
+%pip install numpy
+````
 
 # Valid imports
 

basic_lessons/lesson2_exercise_answers.md

@@ -13,6 +13,12 @@ kernelspec:
 ## I found an issue
 Thank you! Please report it at https://github.com/MarinhoLab/OpenExecutableBooksRobotics/issues
 
+# Package installation
+
+````{code-cell}
+%%capture
+%pip install numpy
+````
 
 # Valid imports
 

basic_lessons/lesson3_exercise_answers.md

@@ -13,6 +13,12 @@ kernelspec:
 ## I found an issue
 Thank you! Please report it at https://github.com/MarinhoLab/OpenExecutableBooksRobotics/issues
 
+# Package installation
+
+````{code-cell}
+%%capture
+%pip install numpy
+````
 
 # Valid imports
 

basic_lessons/lesson4_exercise_answers.md

@@ -13,6 +13,12 @@ kernelspec:
 ## I found an issue
 Thank you! Please report it at https://github.com/MarinhoLab/OpenExecutableBooksRobotics/issues
 
+# Package installation
+
+````{code-cell}
+%%capture
+%pip install numpy
+````
 
 # Valid imports