fix(model_config): improve mobile responsiveness and dropdown boundary constraints

[mdnaimul22]

Summary

This PR improves mobile usability and dropdown layout constraints for the _model_config plugin's model and agent profile switchers.

Changes

• Dropdown Boundaries: Added max-width constraints (max-width: min(320px, calc(100vw - 24px))) and aligned .agent-profile-dropdown to right: 0 to prevent dropdown menus from overflowing viewport edges on mobile devices.
• Flex Layout Stabilization: Set .model-context-strip to flex-wrap: nowrap and anchors to min-width: 0; flex-shrink: 1; to avoid layout breaks on long model/preset names.
• Mobile Styling: Added @media (max-width: 600px) and @media (max-width: 420px) queries with scaled padding, compact font sizing, and dynamic label truncation (max-width: min(130px, 34vw)).

Verification

• Tested dropdown rendering on desktop and responsive mobile viewports (360px–420px widths).
• Verified that long profile and model names truncate gracefully without pushing UI elements off-screen.