add fresh install redirect and admin provider tests

Fresh installs now redirect to /users/register instead of showing the
demo shop. Post-login redirect goes to /admin dashboard (with setup
checklist) instead of /admin/settings. Added 16 provider tests covering
index (list, delete, sync) and form (new, edit, test connection).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

PROGRESS.md

@@ -43,11 +43,11 @@ Plans: [admin-redesign.md](docs/plans/admin-redesign.md) | [setup-wizard.md](doc
 | ~~11~~ | ~~Theme editor back-to-admin link~~ | 6 | 30m | done |
 | ~~4~~ | ~~Admin bar on shop pages~~ | — | 1h | done |
 | ~~12~~ | ~~Consolidate settings page~~ | 6, 7 | 2-3h | done |
+| ~~13~~ | ~~Admin dashboard (+ setup checklist)~~ | 6, 7, 9 | 2h | done |
+| ~~15~~ | ~~Setup wizard + admin tests~~ | 13 | 1.5h | done |
 | | **Next up** | | | |
-| 13 | Admin dashboard (+ setup checklist) | 6, 7, 9 | 2h | |
 | 5 | Search (functional search with results) | — | 3-4h | |
 | | **Needs admin stable** | | | |
-| 15 | Setup wizard + admin tests | 13 | 1.5h | |
 | 16 | Variant refinement with live data | — | 2-3h | |
 | 17 | Wire real product data to shop pages | — | 2-3h | |
 | 18 | Shipping costs at checkout | 17 | 2-3h | |