improve setup UX: password field, setup hook, checklist banners, theme tweaks

- add password field and required shop name to setup wizard
- extract SetupHook for DRY redirect to /setup when no admin exists
- add ?from=checklist param to checklist hrefs with contextual banner on
  email settings and theme pages for easy return to dashboard
- remove email warning banner from admin layout (checklist covers it)
- make email a required checklist item (no longer optional)
- add DevReset module for wiping dev data without restart
- rename "Theme Studio" to "Theme", drop subtitle
- lower theme editor side-by-side breakpoint from 64em to 48em
- clean up login/registration pages (remove dead registration_open code)
- fix settings.put_secret to invalidate cache after write

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

assets/css/admin/components.css

@@ -934,6 +934,25 @@
   border: 1px solid var(--t-border-default);
 }
 
+/* ── Checklist banner (shown when arriving from the launch checklist) ── */
+
+.admin-checklist-banner {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  padding: 0.75rem 1rem;
+  margin-bottom: 1.5rem;
+  font-size: 0.875rem;
+  line-height: 1.5;
+  border-radius: 0.5rem;
+  background-color: color-mix(in oklch, var(--t-status-info) 10%, var(--t-surface-base));
+  border: 1px solid color-mix(in oklch, var(--t-status-info) 20%, var(--t-surface-base));
+
+  & .admin-checklist-banner-icon { color: var(--t-status-info); flex-shrink: 0; }
+  & .admin-checklist-banner-text { flex: 1; color: var(--t-text-secondary); }
+  & .admin-checklist-banner-link { font-weight: 500; white-space: nowrap; }
+}
+
 
 
 /* ── Dashboard stats grid ── */
@@ -3422,7 +3441,7 @@
   min-height: 100vh;
   background: var(--t-surface-sunken);
 
-  @media (min-width: 64em) {
+  @media (min-width: 48em) {
     flex-direction: row;
     height: 100vh;
   }
@@ -3434,7 +3453,7 @@
   flex-shrink: 0;
   transition: width 0.3s, padding 0.3s;
 
-  @media (min-width: 64em) {
+  @media (min-width: 48em) {
     height: 100vh;
   }
 }
@@ -3444,7 +3463,7 @@
   overflow-y: auto;
   padding: 1.5rem;
 
-  @media (min-width: 64em) {
+  @media (min-width: 48em) {
     width: 380px;
   }
 }
@@ -4168,6 +4187,10 @@
   display: flex;
   flex-direction: column;
   gap: 1rem;
+
+  &[hidden] {
+    display: none;
+  }
 }
 
 .admin-adapter-link {