fix: responsive controls panel

[g-eoj]

Summary

• Controls panel now overlays the chat (position: fixed) instead of pushing content aside
• Panel is hidden by default on screens narrower than 1600px and visible on larger screens
• Smooth slide-in/out animation on open and close, matching the feel of the collapsible control sections
• Scrollbar moved to the viewport's right edge by collapsing a redundant wrapper div

Closes #19

Test plan

• On a wide screen (≥ 1600px): panel is open by default, close/reopen with the X and chevron buttons, verify smooth animation
• On a narrow screen (< 1600px): panel is hidden by default, open with the chevron, verify it overlays without shifting chat content
• Confirm the chat scrollbar sits at the far right edge of the viewport

🤖 Generated with Claude Code

Greptile Summary

This PR successfully transforms the controls panel from a static sidebar into a responsive overlay that adapts to screen size. The panel now uses fixed positioning to overlay the chat content instead of pushing it aside, with smooth slide-in/out animations matching the existing collapsible control sections.

Key improvements:

• Panel overlays chat content using position: fixed with z-index: 40
• Automatically hidden on screens < 1600px, visible on larger screens
• Increased panel opacity from 50% to 95% for better readability over content
• 300ms slide animation timing perfectly synchronized between CSS keyframes and JavaScript timeout
• Scrollbar moved to viewport edge by removing redundant wrapper div
• Used 100dvh for mobile compatibility with dynamic viewport changes

The implementation is clean and follows good practices with proper accessibility attributes (title on buttons), well-timed animations, and appropriate signal state management.

Confidence Score: 5/5

• This PR is safe to merge with no issues found
• The changes are well-implemented with proper animation timing, responsive behavior, and no logical errors or security concerns. The code follows established patterns and includes appropriate accessibility features.
• No files require special attention

Important Files Changed

Filename	Overview
web/assets/styles.css	Updated panel styling for fixed overlay positioning, increased opacity to 95%, and added smooth slide-in/out animations
web/islands/Chat.tsx	Removed redundant wrapper div and moved scrollbar to viewport edge by consolidating flex layout
web/islands/ControlsPanel.tsx	Added responsive behavior to hide panel on screens < 1600px, implemented close animation with 300ms timing, and dynamic class management

_{Last reviewed commit: c55a589}