feat: implement mobile terminal UX

- Add mobile viewport detection hook
- Add virtual keyboard detection with fallback
- Add auto-hide hook for header/keys strip
- Add special keys mapping hook
- Create MobileTerminalHeader, SpecialKeysStrip, SpecialKeysPanel components
- Create MobileTerminalWrapper component
- Update TerminalComponent with mobile support, font scaling, copy/paste, reconnection
- Update AppShell to hide chrome on mobile terminal pages
- Update TerminalPage to use MobileTerminalWrapper
- Add comprehensive mobile terminal styles
- TypeScript check passes
- Build succeeds

openspec/changes/mobile-terminal-ux/specs/frontend-foundation/spec.md

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+## MODIFIED Requirements
+
+### Requirement: Layout Component
+
+The system SHALL provide a consistent application layout for authenticated screens across desktop and mobile sizes.
+
+#### Scenario: Application shell
+- **GIVEN** the frontend application
+- **THEN** a Layout component SHALL:
+  - Display a header with user info and logout
+  - Display sidebar navigation on desktop
+  - Show main content area
+  - Collapse sidebar into a mobile menu toggle on small viewports
+  - **AND** on mobile terminal pages, provide a minimal collapsible header instead of the full AppShell
+
+#### Scenario: Terminal page mobile layout
+- **GIVEN** a user on a terminal page on a mobile device
+- **WHEN** the page loads
+- **THEN** the full AppShell is replaced with a minimal header
+- **AND** the header contains: back button, menu toggle, instance name, close button
+- **AND** the header auto-hides after 3 seconds of inactivity
+- **AND** tapping the terminal area toggles header visibility
+- **AND** the sidebar navigation is accessible via the menu toggle