fix: move URL install confirmation prompt before spinner (#2783) (#2784)

* fix: move URL install confirmation prompt before spinner (#2783)

The typer.confirm() prompt inside console.status() was overwritten by
Rich's spinner animation, making extension add --from <url> appear hung.

Move URL validation and the default-deny confirmation prompt before the
spinner block so the user can see and respond to the [y/N] prompt.

* Potential fix for pull request finding

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* fix: guard prompt with not dev, escape from_url in Rich markup

Address PR review feedback:
- Gate URL confirmation prompt on 'not dev' so --dev + --from does not
  show a confusing prompt for a URL path that will be ignored.
- Escape from_url with rich.markup.escape() in both the warning panel
  and the download message to prevent markup injection via crafted URLs.

* fix: remove unused import, reuse safe_url, add regression tests

Address second round of PR review:
- Remove unused urllib.request import from URL install path
- Remove redundant re-import of rich.markup.escape; reuse safe_url
  computed before the spinner for download and error messages
- Add test_add_from_url_prompts_before_spinner: asserts typer.confirm
  fires before console.status spinner to prevent #2783 regression
- Add test_add_from_url_cancel_exits_cleanly: asserts declining the
  prompt exits with code 0 and prints Cancelled

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