fix(modules-2,6,7,8,9,10,14): deterministic main branch + correct two claims

- M2 lab now `git init -b main` (with older-git fallback note) so every later
  `main` reference resolves; reconciled M3/M6/M7/M8 wording and M10's standalone
  review-lab repo (`git init -qb main`).
- M9: replace "issues are on by default on every forge" with a provider-neutral
  version naming the exceptions (Bitbucket/Azure DevOps/SourceHut).
- M14: qualify "hosted runners need zero setup" — true for SaaS forges; the
  self-hosted track needs a runner attached (Module 19). Both paths stay valid.

Closes #5
Closes #13
Closes #16

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TfzV5QvtPDz8LJS3Pu5VLT

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

@@ -206,7 +206,7 @@ real change, then review a diff the "AI" produced and catch the trap planted in
    ```bash
    mkdir -p ~/workflow-course/review-lab && cd ~/workflow-course/review-lab
    cp /path/to/modules/10-reviewing-code-you-didnt-write/lab/tasks-app/*.py .
-   git init -q && git add . && git commit -qm "base: tasks-app"
+   git init -qb main && git add . && git commit -qm "base: tasks-app"   # -b main so the git switch main / git diff main.. steps below resolve
 
    python cli.py add "write the review module"
    python cli.py done 99        # baseline: prints "error: no task at index 99", exits non-zero