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/shared/components/ui/button/button.html

@@ -0,0 +1,3 @@
+<button [type]="type()" class="ev-button" [class]="'ev-button--' + variant()" [disabled]="disabled()">
+  <ng-content></ng-content>
+</button>

apps/frontend/src/app/shared/components/ui/button/button.scss

@@ -0,0 +1,51 @@
+.ev-button {
+  width: 100%;
+  padding: 0.7rem;
+  border: none;
+  border-radius: var(--radius-sm);
+  font-size: 0.95rem;
+  font-weight: 600;
+  font-family: var(--font-family);
+  cursor: pointer;
+
+  &:disabled {
+    cursor: not-allowed;
+    opacity: 0.7;
+  }
+}
+
+.ev-button--primary {
+  background: var(--color-primary);
+  color: #fff;
+
+  &:disabled {
+    background: var(--color-disabled);
+  }
+
+  &:not(:disabled):hover {
+    background: var(--color-primary-hover);
+  }
+}
+
+.ev-button--secondary {
+  background: var(--color-surface);
+  border: 1px solid var(--color-border);
+  color: var(--color-label);
+
+  &:not(:disabled):hover {
+    background: var(--color-bg);
+  }
+}
+
+.ev-button--danger {
+  background: var(--color-danger);
+  color: #fff;
+
+  &:disabled {
+    background: var(--color-disabled);
+  }
+
+  &:not(:disabled):hover {
+    background: #b91c1c;
+  }
+}

apps/frontend/src/app/shared/components/ui/button/button.spec.ts

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+import { Component } from '@angular/core';
+import { TestBed } from '@angular/core/testing';
+import { Button } from './button';
+
+@Component({
+  standalone: true,
+  imports: [Button],
+  template: `<ev-button>Valider</ev-button>`,
+})
+class ButtonHost {}
+
+describe('Button', () => {
+  beforeEach(async () => {
+    await TestBed.configureTestingModule({ imports: [Button] }).compileComponents();
+  });
+
+  it('applique la classe de la variante primary par défaut', () => {
+    const fixture = TestBed.createComponent(Button);
+    fixture.detectChanges();
+
+    const button = fixture.nativeElement.querySelector('button');
+    expect(button.classList).toContain('ev-button--primary');
+  });
+
+  it('applique la classe de la variante demandée', () => {
+    const fixture = TestBed.createComponent(Button);
+    fixture.componentRef.setInput('variant', 'danger');
+    fixture.detectChanges();
+
+    const button = fixture.nativeElement.querySelector('button');
+    expect(button.classList).toContain('ev-button--danger');
+  });
+
+  it('désactive le bouton natif quand disabled est vrai', () => {
+    const fixture = TestBed.createComponent(Button);
+    fixture.componentRef.setInput('disabled', true);
+    fixture.detectChanges();
+
+    const button = fixture.nativeElement.querySelector('button');
+    expect(button.disabled).toBe(true);
+  });
+
+  it('projette le contenu', async () => {
+    await TestBed.configureTestingModule({ imports: [ButtonHost] }).compileComponents();
+    const fixture = TestBed.createComponent(ButtonHost);
+    fixture.detectChanges();
+
+    expect(fixture.nativeElement.querySelector('button').textContent).toContain('Valider');
+  });
+});

apps/frontend/src/app/shared/components/ui/button/button.ts

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+import { Component, input } from '@angular/core';
+
+export type ButtonVariant = 'primary' | 'secondary' | 'danger';
+
+@Component({
+  selector: 'ev-button',
+  standalone: true,
+  templateUrl: './button.html',
+  styleUrl: './button.scss',
+})
+export class Button {
+  variant = input<ButtonVariant>('primary');
+  type = input<'button' | 'submit'>('button');
+  disabled = input(false);
+}