Responsive Design Breakpoint Rationale Document

Document the responsive breakpoint strategy for {{product_name}}.

For each breakpoint—mobile ({{mobile_px}}px), tablet ({{tablet_px}}px), desktop ({{desktop_px}}px), etc.:
1. Rationale: What device(s) does this target? Market share data if available.
2. Layout shift: What changes here? (Single col → 2 col → 3 col?)
3. User behavior: How does the task/interaction differ on this device?
4. Touch vs. pointer: Implications for button size, spacing, gesture support?
5. Performance: Image resolution, asset loading strategy per breakpoint
6. Testing focus: What specific scenarios must be tested at this breakpoint?

Defend why you chose these specific widths, not others.