fix: enlarge close button hit area to fix unreliable click

[quiet-node]

Summary

• Close button was only 12x12px, causing near-misses to trigger startDragging() on the adjacent non-interactive area
• Near-misses either moved the window (shifting the button away) or caused macOS to consume the subsequent click event
• Fix: expand hit area to ~24x24px via p-1.5 -m-1.5 on the button wrapper; visual dot stays 12x12px via inner div; negative margin preserves flex spacing

Test Plan

• Open Thuki overlay, send a message to enter chat mode
• Click the red close dot once — overlay should hide reliably on first click
• Verify visual appearance is unchanged (12px red dot, × icon on hover)
• Verify hover scale and active press animations still work
• bun run test passes (462 tests)
• bun run validate-build passes with zero warnings/errors