fix(panel): GUI defects from the 1.2.x layout pass (P3)

- .flash.error now renders on the danger surface instead of the success
  one; RateLimitErr previously showed as green with red text.
- User delete goes through a confirmation page (GET/POST
  /users/{uid}/delete), matching the domain-delete pattern, instead of a
  plain submit button next to Save with no confirmation.
- Extracted the repeated DNS Host/Type/Value markup on a domain's page and
  the duplicated Settings credentials form into shared partials. No
  behaviour change.

docs/plans/code-review.md P3 checked off; CHANGELOG updated.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/web/view/view.go

@@ -37,6 +37,7 @@ var pageFiles = map[string][]string{
 	"settings":      {"templates/settings.html"},
 	"users":         {"templates/users.html"},
 	"user_form":     {"templates/user_form.html"},
+	"user_delete":   {"templates/user_delete.html"},
 	"backup":        {"templates/backup.html", "templates/encrypt_fields.html"},
 	"domain_detail": {"templates/domain_detail.html", "templates/encrypt_fields.html"},
 	"domain_delete": {"templates/domain_delete.html"},