chore: remove unused components and markup-only tests

- Delete Blade components, component classes, Livewire components and
  views that nothing uses after the redesign.
- Delete tests that only compare Blade/CSS source text; keep the source
  checks for authorization gates, stable wire:key values and escaping.
- Update stale tests to the current UI and behaviour.
- Update DESIGN.md to the current navigation and layout.
- Add a lesson: test behaviour, not source markup.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/Unit/InstallScriptRockyDockerRepoTest.php

@@ -2,7 +2,7 @@
 
 function expectRockyInstallScriptToUseRhelRepo(string $path): void
 {
-    $installScript = file_get_contents(base_path($path));
+    $installScript = file_get_contents(dirname(__DIR__, 2).'/'.$path);
 
     expect($installScript)
         ->toContain('install_docker_from_rhel_repo() {')