fix: resolve all DaisyUI audit issues

- settings.js: replace broken CSS vars with getThemeColor() helper
- base.html: add bg-primary text-primary-content active state to drawer
- All templates: btn-small -> btn-sm (DaisyUI standard)
- Delete orphan templates/components/header.html
- auth-utils.js: fix .show class -> use hidden (Tailwind)
- login.html: remove redundant auth-* classes, keep DaisyUI only
- auth-ui.js: update form selector for cleanup
- watchlist.html: fix nav active class styling
- 4 JS files (series-search, tabs, recommendations, anime-details):
  - Replace all old CSS classes with DaisyUI/Tailwind
  - Remove hardcoded colors, use theme-aware classes
  - loading-spinner -> DaisyUI loading component
  - no-results/search-results -> Tailwind utility layout
  - All badges -> DaisyUI badge variants

static/js/auth-ui.js

@@ -102,7 +102,7 @@ function resetLoading(buttonId, originalText) {
 
 function switchTab(tab) {
   const tabs = document.querySelectorAll('.auth-tab');
-  const forms = document.querySelectorAll('.auth-form');
+  const forms = document.querySelectorAll('#loginForm, #registerForm');
 
   // Remove active states — DaisyUI uses tab-active on tabs, hidden on forms
   tabs.forEach(t => t.classList.remove('tab-active'));