fix(setup): stop fork clones from filing issues on the upstream repo by default (#389) (#392)

gh repo fork --clone - SETUP.md's own fork command - sets the upstream
repo as gh's default repository, which gh uses for creating issues and
PRs. A user's own automation running gh issue create from a fork clone
therefore published personal job-search data on the upstream public
tracker. SETUP.md section 2 now includes gh repo set-default in the fork
commands with a point-of-decision warning, and .github/ISSUE_TEMPLATE/
carries the same heads-up the PR template already had for the web path.
Blank issues stay enabled.

SETUP.md

@@ -158,10 +158,19 @@ If a command still uses `pdftotext -layout`, it must pass `-enc UTF-8` as well.
 ```bash
 gh repo fork MadsLorentzen/ai-job-search --clone
 cd ai-job-search
+gh repo set-default <your-github-username>/ai-job-search
 ```
 
 Or manually: fork on GitHub, then clone your fork.
 
+> **The `set-default` line is not optional.** `gh repo fork --clone` sets the
+> **upstream** repo as gh's default repository ("The `upstream` remote will be set as
+> the default remote repository" — `gh repo fork --help`), and gh uses the default for
+> **creating issues and PRs**. Without it, any later `gh issue create` run from this
+> clone — by you or by an agent you have asked to track your applications — silently
+> files on the upstream **public** tracker, publishing whatever the issue contains
+> under your GitHub identity, on a repo where you cannot delete it (#389).
+
 > **Before you go further: forks are public.** GitHub cannot make a fork of a public
 > repository private, and `/setup` (section 6) writes your personal data into **tracked**
 > files — pushing those commits to a fork publishes them. If this copy is for your own