Use python3 as the canonical command name course-wide (#104) (#105)

capstone/README.md

@@ -47,7 +47,7 @@ already standing; it doesn't re-pour the foundation.
 Pick something small enough to finish in one sitting and real enough to touch the whole stack. We'll
 add **due dates**:
 
-- A task can carry an optional due date: `python cli.py add "file taxes" --due <YYYY-MM-DD>`.
+- A task can carry an optional due date: `python3 cli.py add "file taxes" --due <YYYY-MM-DD>`.
 - A new `overdue` command lists pending tasks whose due date has already passed.
 - The deployed service grows a matching `GET /overdue` endpoint, so the change is visible in the
   running container, not just the CLI.
@@ -184,9 +184,9 @@ agent), your forge account, and a working Docker install.
    in the future, one safely in the past) so the assertion below holds whenever you run this:
 
    ```bash
-   python cli.py add "file taxes" --due <a date a few months out>   # future → NOT overdue
-   python cli.py add "renew domain" --due 2020-01-01                # past   → overdue
-   python cli.py overdue        # should list "renew domain", not "file taxes"
+   python3 cli.py add "file taxes" --due <a date a few months out>   # future → NOT overdue
+   python3 cli.py add "renew domain" --due 2020-01-01                # past   → overdue
+   python3 cli.py overdue        # should list "renew domain", not "file taxes"
    ```
 
    > *Verify-before-publish: refresh the example due dates so the "future" one is still in the future
@@ -199,7 +199,7 @@ agent), your forge account, and a working Docker install.
    them by name. Confirm the suite is green:
 
    ```bash
-   pytest        # or: python -m unittest
+   pytest        # or: python3 -m unittest
    ```
 
    Once it's green, tell the AI to commit the change. Then verify what it actually staged and wrote: