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

templates/login.html

@@ -23,17 +23,17 @@
                 </div>
 
                 <!-- Error / Success Alerts -->
-                <div id="authError" class="auth-error alert alert-error hidden mb-2" role="alert" aria-live="polite">
+                <div id="authError" class="alert alert-error hidden mb-2" role="alert" aria-live="polite">
                     <i class="fa-solid fa-circle-exclamation"></i>
                     <span></span>
                 </div>
-                <div id="authSuccess" class="auth-success alert alert-success hidden mb-2" role="status" aria-live="polite">
+                <div id="authSuccess" class="alert alert-success hidden mb-2" role="status" aria-live="polite">
                     <i class="fa-solid fa-circle-check"></i>
                     <span></span>
                 </div>
 
                 <!-- Login Form -->
-                <form class="auth-form active" id="loginForm">
+                <form id="loginForm">
                     <div class="form-control mb-3">
                         <label class="label" for="loginUsername">
                             <span class="label-text">Nom d'utilisateur</span>
@@ -68,7 +68,7 @@
                 </form>
 
                 <!-- Register Form -->
-                <form class="auth-form hidden" id="registerForm">
+                <form class="hidden" id="registerForm">
                     <div class="form-control mb-3">
                         <label class="label" for="registerUsername">
                             <span class="label-text">Nom d'utilisateur</span>