fix(chat): adjust the position of timeline jump rail

[XNgZIyX]

Summary

• Adjust the chat timeline jump rail position so it avoids the right-side workbench rail and panels.

Why

• The timeline jump rail was positioned with a fixed viewport offset, which could overlap or crowd the right-side workbench toolbar.
• When right-side panels are opened, the jump rail should keep a stable relative distance from the active panel boundary.

Changes

• Added a timelineJumpRailRightOffset prop to MessageTimeline.
• Passed the offset through WorkbenchChatStage.
• Calculated the right-side offset in WorkbenchConversationStage based on the workbench rail and right-side panel state.
• Updated timeline-jump-rail CSS to use a configurable CSS variable with a fallback offset.

Media

Tests

• No unit tests added because this is a layout-only UI adjustment.

Validation

• [√] I agree that this contribution is submitted under the Contributor License Agreement.
• [√] npm run test
• [√] npm run typecheck
• [√] npm run build
• [√] npm run dev (if runtime or UI behavior changed)
• [√] UI change: video or GIF attached

[XingYu-Zhong]

我们改了样式