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

Most current systems (default Debian/Ubuntu, recent macOS) install Python
only as `python3`, with no bare `python` on PATH, so learners who copied
`python cli.py ...` into their host shell hit "command not found".

Convert host-shell `python <cmd>` -> `python3 <cmd>` across module/lab
READMEs, lab `.py` docstrings & usage strings, blog posts, lab prompt and
instruction files, the M04 verify.sh message, and the M10/M24 lab patches.
Module 01's convention note (and its blog/02 mirror) is rewritten so
`python3` is canonical and `python` is the documented fallback.

Stop-lines respected: Docker image tags (`python:3.12-slim`), `.venv/.../python`
and `...\.venv\Scripts\python.exe` paths, the M20 `"command": "python"`
teaching example and surrounding venv prose, container-internal invocations
(M16/M18 Dockerfiles, M16 README `docker run` examples), and CI-workflow
`run:` steps fed by `actions/setup-python` / `image: python:3.12` are left
as `python` on purpose.

pip was left out of scope: most occurrences are prose or CI/container-internal,
and `pip3` does not fix the PEP 668 externally-managed-environment refusal that
the course already addresses with venvs. The M01 note is worded to stay
consistent with bare `pip` (use whichever pip pairs with your Python).

Build (tools/build_wiki.py) and tools/check.sh both pass.

Closes #104

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GAEzanEoGJT5o1VizQar47

modules/24-assistive-agents/README.md

@@ -184,7 +184,7 @@ This is the real production loop with the forge plumbing simulated locally.
 
 **You'll need:**
 
-- Python 3.10+ (`python --version`).
+- Python 3.10+ (`python3 --version`).
 - The lab files in `~/ai-workflow-course/modules/24-assistive-agents/lab/`.
 - Claude Code (`claude --version`; sub your own agent), the editor/CLI agent from Module 4.
 
@@ -205,7 +205,7 @@ it runs the scripts and writes the files. You verify at the gate.
 
    ```
    You: In ~/ai-workflow-course/modules/24-assistive-agents/lab, run
-        `python reviewer.py apply ai-review.sample.json` and show me the output.
+        `python3 reviewer.py apply ai-review.sample.json` and show me the output.
    ```
 
    Read what comes back: comments sorted by severity, a recommendation, and then the **human decision
@@ -215,7 +215,7 @@ it runs the scripts and writes the files. You verify at the gate.
    the reviewer, and write its JSON review to a file:
 
    ```
-   You: Run `python reviewer.py prompt`, follow the rubric in that output to review the diff, and
+   You: Run `python3 reviewer.py prompt`, follow the rubric in that output to review the diff, and
         save your review as JSON to my-review.json.
    ```
 
@@ -226,7 +226,7 @@ it runs the scripts and writes the files. You verify at the gate.
 3. Have the agent render its own review through the gate:
 
    ```
-   You: Run `python reviewer.py apply my-review.json` and show me the result.
+   You: Run `python3 reviewer.py apply my-review.json` and show me the result.
    ```
 
 4. **Make the human decision. This part stays yours.** Open `feature.patch` and check the agent's
@@ -243,7 +243,7 @@ A new issue just arrived: `sample-issue.md` (the `done` command crashes on an em
 1. See the loop with the canned response:
 
    ```
-   You: Run `python triage.py apply ai-triage.sample.json` and show me the output.
+   You: Run `python3 triage.py apply ai-triage.sample.json` and show me the output.
    ```
 
    Read the suggested labels, the route, and the **human confirm gate**. The agent applied nothing.
@@ -252,14 +252,14 @@ A new issue just arrived: `sample-issue.md` (the `done` command crashes on an em
    and save its suggestion:
 
    ```
-   You: Run `python triage.py prompt`, follow it to triage the issue using only the committed
+   You: Run `python3 triage.py prompt`, follow it to triage the issue using only the committed
         taxonomy, and save your JSON suggestion to my-triage.json.
    ```
 
 3. Render the suggestion through the gate:
 
    ```
-   You: Run `python triage.py apply my-triage.json` and show me the result.
+   You: Run `python3 triage.py apply my-triage.json` and show me the result.
    ```
 
 4. **Watch the guardrail.** The script validates every suggested label against the committed
@@ -340,8 +340,8 @@ This is expansion-zone material; the agent-tooling landscape moves fast. Re-chec
       merge/close, so comment/label-only is actually grantable? Name two that do.
 - [ ] Is the turnkey "AI review bot / app" framing still accurate, or has the dominant pattern shifted
       (e.g. baked into the forge, or into editor agents)? Keep the description vendor-neutral.
-- [ ] Confirm the lab scripts run on a current Python (`python reviewer.py apply ai-review.sample.json`
-      and `python triage.py apply ai-triage.sample.json`) with no dependencies.
+- [ ] Confirm the lab scripts run on a current Python (`python3 reviewer.py apply ai-review.sample.json`
+      and `python3 triage.py apply ai-triage.sample.json`) with no dependencies.
 - [ ] Re-verify the cross-references resolve to the right module numbers (9, 10, 13, 14, 15, 22, 25)
       if any modules were renumbered.
 - [ ] Check that nothing here pins a specific LLM vendor or a specific bot's config filename.