feat(frontend): design système - tokens, composants ui et restylage des pages

Centralise les couleurs/rayons/espacements dispersés en dur dans chaque page
(login, change-password, dashboard) en tokens CSS partagés, ajoute un petit
set de composants standalone réutilisables (ev-button, ev-card, ev-alert,
ev-badge) et intègre le logo EnerVision en en-tête des pages ainsi que dans
Swagger/ReDoc côté backend.

Refs #91

apps/frontend/src/app/features/auth/login/login.scss

@@ -3,79 +3,41 @@
   align-items: center;
   justify-content: center;
   min-height: 100vh;
-  background: #f3f4f6;
-  font-family: 'Segoe UI', system-ui, sans-serif;
+  background: var(--color-bg);
 }
 
-.auth-card {
-  background: #ffffff;
-  border: 1px solid #e5e7eb;
-  border-radius: 12px;
-  padding: 2.5rem;
+.auth-card-wrapper {
   width: 100%;
   max-width: 360px;
-  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.06);
-  display: flex;
-  flex-direction: column;
-
-  h1 {
-    margin: 0;
-    font-size: 1.5rem;
-    font-weight: 700;
-    color: #1f2937;
-  }
-
-  .auth-subtitle {
-    margin: 0.25rem 0 1.5rem;
-    color: #6b7280;
-    font-size: 0.9rem;
-  }
-
-  label {
-    font-size: 0.85rem;
-    font-weight: 600;
-    color: #374151;
-    margin-bottom: 0.35rem;
-    margin-top: 1rem;
-  }
-
-  input {
-    padding: 0.6rem 0.75rem;
-    border: 1px solid #d1d5db;
-    border-radius: 8px;
-    font-size: 0.95rem;
-
-    &:focus {
-      outline: none;
-      border-color: #3b82f6;
-      box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.15);
-    }
-  }
-
-  button {
-    margin-top: 1.5rem;
-    padding: 0.7rem;
-    background: #3b82f6;
-    color: #fff;
-    border: none;
-    border-radius: 8px;
-    font-size: 0.95rem;
-    font-weight: 600;
-    cursor: pointer;
-
-    &:disabled {
-      background: #9ca3af;
-      cursor: not-allowed;
-    }
-
-    &:not(:disabled):hover {
-      background: #2563eb;
-    }
-  }
 }
 
-.auth-error {
-  margin: 0.75rem 0 0;
-  color: #dc2626;
-  font-size: 0.85rem;
+.auth-logo {
+  display: block;
+  height: 48px;
+  margin: 0 auto 1rem;
+}
+
+h1 {
+  margin: 0;
+  font-size: 1.5rem;
+  font-weight: 700;
+  color: var(--color-text);
+  text-align: center;
+}
+
+.auth-subtitle {
+  margin: 0.25rem 0 1.5rem;
+  color: var(--color-text-muted);
+  font-size: 0.9rem;
+  text-align: center;
+}
+
+ev-alert {
+  display: block;
+  margin-top: 0.75rem;
+}
+
+ev-button {
+  display: block;
+  margin-top: 1.5rem;
 }