feat(cua-driver): animate drag as a continuous point-to-point gesture

[f-trycua]

Problem

The agent cursor currently represents drag with the same general movement treatment used for ordinary pointer travel. During a real drag, this does not clearly communicate the gesture from source to destination or distinguish press, hold, travel, and release.

Desired behavior

Render a drag as one continuous point-to-point gesture driven by the real action arguments:

1. Move to the source point.
2. Enter the drag state when the button is pressed.
3. Keep the drag treatment active while the overlay follows the dispatched path from from_x/from_y to to_x/to_y.
4. Show a subtle release or drop response at the destination.
5. Return to idle only after the real action completes.

The animation should use duration_ms and steps where available so the overlay stays synchronized with the dispatched gesture instead of playing a separate generic glide.

Requirements

• Preserve the drag semantic icon throughout the held movement.
• Avoid a generic move animation or visual teleport between the source and destination.
• Compose correctly with background/foreground, AX/pixel, browser/desktop, and session-color treatments.
• Support left, right, and middle-button drag variants without requiring separate themes.
• Respect reduced-motion mode with an understandable low-motion fallback.
• Keep the behavior consistent across macOS, Windows, and Linux renderers.
• Keep custom cursor themes compatible through the existing semantic drag state rather than adding a required new icon.

Acceptance criteria

• A real drag action visibly traverses the complete source-to-destination path while the drag state remains active.
• Press, travel, and release phases are ordered and synchronized with native input delivery.
• The action gallery includes a deterministic point-to-point drag preview.
• Automated tests cover interpolation, lifecycle ordering, reduced motion, and modifier composition.
• Cross-platform video or visual evidence confirms the result on macOS, Windows, and Linux.