feat: Conversion CSS mobile-first des layouts et pages admin

L'ensemble du frontend utilisait un mix de @media (max-width) desktop-first
et @media (min-width) mobile-first, en contradiction avec la spec UX qui
impose une stratégie mobile-first radicale (78% des parents/élèves sur mobile).

Cette conversion uniformise les 8 fichiers restants vers @media (min-width)
avec les breakpoints de la spec UX (sm: 640px, md: 768px) pour garantir
une expérience progressive enhancement cohérente.

frontend/tests/unit/lib/features/sessions/api/sessions.test.ts

@@ -0,0 +1,159 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+
+/**
+ * Unit tests for the sessions API module.
+ *
+ * Tests getSessions(), revokeSession(), and revokeAllSessions() which all
+ * rely on authenticatedFetch from $lib/auth and getApiBaseUrl from $lib/api.
+ */
+
+// Mock $lib/api
+vi.mock('$lib/api', () => ({
+	getApiBaseUrl: () => 'http://test.classeo.local:18000/api'
+}));
+
+// Mock $lib/auth
+const mockAuthenticatedFetch = vi.fn();
+vi.mock('$lib/auth', () => ({
+	authenticatedFetch: (...args: unknown[]) => mockAuthenticatedFetch(...args)
+}));
+
+import { getSessions, revokeSession, revokeAllSessions } from '$lib/features/sessions/api/sessions';
+
+describe('sessions API', () => {
+	beforeEach(() => {
+		vi.clearAllMocks();
+	});
+
+	afterEach(() => {
+		vi.restoreAllMocks();
+	});
+
+	// ==========================================================================
+	// getSessions
+	// ==========================================================================
+	describe('getSessions', () => {
+		it('should return session array on success', async () => {
+			const mockSessions = [
+				{
+					family_id: 'family-1',
+					device: 'Desktop',
+					browser: 'Chrome',
+					os: 'Linux',
+					location: 'Paris, France',
+					created_at: '2025-01-15T10:00:00Z',
+					last_activity_at: '2025-01-15T12:00:00Z',
+					is_current: true
+				},
+				{
+					family_id: 'family-2',
+					device: 'Mobile',
+					browser: 'Safari',
+					os: 'iOS',
+					location: 'Lyon, France',
+					created_at: '2025-01-14T08:00:00Z',
+					last_activity_at: '2025-01-14T09:00:00Z',
+					is_current: false
+				}
+			];
+
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: true,
+				json: () => Promise.resolve({ sessions: mockSessions })
+			});
+
+			const result = await getSessions();
+
+			expect(mockAuthenticatedFetch).toHaveBeenCalledWith(
+				'http://test.classeo.local:18000/api/me/sessions'
+			);
+			expect(result).toHaveLength(2);
+			expect(result[0]!.family_id).toBe('family-1');
+			expect(result[0]!.is_current).toBe(true);
+			expect(result[1]!.family_id).toBe('family-2');
+		});
+
+		it('should throw Error when the API response is not ok', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: false,
+				status: 500
+			});
+
+			await expect(getSessions()).rejects.toThrow('Failed to fetch sessions');
+		});
+	});
+
+	// ==========================================================================
+	// revokeSession
+	// ==========================================================================
+	describe('revokeSession', () => {
+		it('should complete without error on success', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: true,
+				status: 204
+			});
+
+			await expect(revokeSession('family-abc')).resolves.toBeUndefined();
+
+			expect(mockAuthenticatedFetch).toHaveBeenCalledWith(
+				'http://test.classeo.local:18000/api/me/sessions/family-abc',
+				expect.objectContaining({ method: 'DELETE' })
+			);
+		});
+
+		it('should throw "Cannot revoke current session" on 403', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: false,
+				status: 403
+			});
+
+			await expect(revokeSession('current-family')).rejects.toThrow(
+				'Cannot revoke current session'
+			);
+		});
+
+		it('should throw generic error on other failure status', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: false,
+				status: 500
+			});
+
+			await expect(revokeSession('family-xyz')).rejects.toThrow(
+				'Failed to revoke session'
+			);
+		});
+	});
+
+	// ==========================================================================
+	// revokeAllSessions
+	// ==========================================================================
+	describe('revokeAllSessions', () => {
+		it('should return revoked_count on success', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: true,
+				json: () =>
+					Promise.resolve({
+						message: '3 sessions revoked',
+						revoked_count: 3
+					})
+			});
+
+			const result = await revokeAllSessions();
+
+			expect(mockAuthenticatedFetch).toHaveBeenCalledWith(
+				'http://test.classeo.local:18000/api/me/sessions',
+				expect.objectContaining({ method: 'DELETE' })
+			);
+			expect(result).toBe(3);
+		});
+
+		it('should throw Error when the API response is not ok', async () => {
+			mockAuthenticatedFetch.mockResolvedValueOnce({
+				ok: false,
+				status: 500
+			});
+
+			await expect(revokeAllSessions()).rejects.toThrow('Failed to revoke all sessions');
+		});
+	});
+});