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/templates/user_form.html

@@ -33,10 +33,13 @@
     </fieldset>
 
     <button type="submit">{{if .IsEdit}}Save{{else}}Create{{end}}</button>
-    {{if .IsEdit}}
-    <button type="submit" name="action" value="delete" class="danger"{{if .LastGlobalLocked}} disabled{{end}}>Delete user</button>
-    {{if .LastGlobalLocked}}<p class="muted">The only global administrator cannot be deleted.</p>{{end}}
-    {{end}}
   </form>
+  {{if .IsEdit}}
+  {{if .LastGlobalLocked}}
+  <p class="muted">The only global administrator cannot be deleted.</p>
+  {{else}}
+  <a class="danger" href="/users/{{.UserID}}/delete">Delete user</a>
+  {{end}}
+  {{end}}
 </div>
 {{end}}