design: session management and devices view

[sanmipaul]

Closes #169

Summary

Implements the Session Management and Active Devices settings view with:

• Device listing with icons (desktop/mobile/tablet), browser/OS info, location, last active timestamp, and IP address
• Current session badge indicator
• Per-row Revoke action with destructive confirm dialog
• "Sign out of all other devices" bulk action
• Empty state when no sessions remain
• Screen reader live region for action announcements
• WCAG 2.1 AA compliance (focus trapping, ARIA roles, keyboard navigation, high contrast support, reduced motion)

Implementation Details

• Route: /settings/sessions
• Component: src/components/SessionManagement/SessionManagement.tsx
• Styles: src/components/SessionManagement/SessionManagement.css
• Uses the existing glass-card pattern and design tokens
• Confirm dialog with focus trap and Escape-to-close (same pattern as KeyboardShortcutsOverlay)
• Responsive: stack layout on mobile, row layout on desktop
• Mock data for 4 devices (current session + 3 others)

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