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

modules/10-reviewing-code-you-didnt-write/README.md

@@ -243,8 +243,8 @@ real change, then review a diff the "AI" produced and catch the trap planted in
    Then see the baseline behavior with your own eyes, because the trap is going to change it:
 
    ```bash
-   python cli.py add "write the review module"
-   python cli.py done 99        # baseline: prints "error: no task at index 99", exits non-zero
+   python3 cli.py add "write the review module"
+   python3 cli.py done 99        # baseline: prints "error: no task at index 99", exits non-zero
    echo "exit code: $?"
    ```
 
@@ -296,12 +296,12 @@ real change, then review a diff the "AI" produced and catch the trap planted in
 5. Now verify your read by running the *failure* path, not the happy one:
 
    ```bash
-   python cli.py add "a real task"
-   python cli.py delete 0        # the requested feature: works fine on the happy path
-   python cli.py add "another"
-   python cli.py done 99         # the trap: compare this to your Part A baseline
+   python3 cli.py add "a real task"
+   python3 cli.py delete 0        # the requested feature: works fine on the happy path
+   python3 cli.py add "another"
+   python3 cli.py done 99         # the trap: compare this to your Part A baseline
    echo "exit code: $?"
-   python cli.py list            # did task 99 (which doesn't exist) get marked done? did anything?
+   python3 cli.py list            # did task 99 (which doesn't exist) get marked done? did anything?
    ```
 
    In the base app, `done 99` was a clean error with a non-zero exit. After this "add a delete