fix: refine component interactions and surfaces

[starc007]

Summary

• synchronize tab label contrast with the moving indicator
• replace the animated input caret with the native caret and expose configurable input slots
• use background surfaces for the bottom sheet and morphing modal
• refine the feedback widget opening and closing morph with staged focus and reduced-motion support

Validation

• bun run typecheck
• bun run lint (passes with one pre-existing non-null assertion warning)
• bun run check:registry
• bun test (22 passing)