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/07-worktrees-running-agents-in-parallel/README.md

@@ -220,7 +220,8 @@ collide. Then you'll merge both back and clean up.
 **You'll need:**
 
 - The `tasks-app` Git repo from Module 2 (initialized, with a few commits). If you skipped ahead,
-  `git init` it and make one commit first.
+  run `git init -b main` and make one commit first — the `-b main` matches Module 2, so the
+  `git switch main` steps below resolve.
 - Git 2.5 or newer (worktrees landed in 2.5; any modern Git is fine — `git --version` to check).
 - **Two** editor-integrated AI sessions you can run at once (Module 4) — two editor windows, or two
   terminal AI sessions. If you only have a browser chat, you can still do the lab; just treat each