## ADDED Requirements

### Requirement: Core layout is device-agnostic and responsive
The system SHALL render key surfaces (header, hero, feed, modal, footer) responsively across mobile, tablet, and desktop viewports.

#### Scenario: Mobile layout behavior
- **WHEN** a user opens the site on a mobile viewport
- **THEN** content remains readable without horizontal overflow
- **AND** interactive controls remain reachable and usable

#### Scenario: Desktop and tablet adaptation
- **WHEN** a user opens the site on tablet or desktop viewports
- **THEN** layout reflows according to breakpoint design rules
- **AND** no key content or controls are clipped
