[Feature Request] Add Zoom Slider and "Fit to Screen" Button for Timeline #56

Description:
Implement timeline zoom controls (Slider and Fit button) on the editor UI to enhance user navigation and project timeline management.

Functional Requirements:

• Zoom Slider:A horizontal slider flanked by magnifying glass icons (- and +).
• Dragging right zooms in for frame-by-frame detailed editing.
• Dragging left zooms out for a broader view.

Fit Button:

• A dedicated button featuring a "Fit to Screen" icon (e.g., outward-pointing arrows).
• Upon clicking, the timeline scale automatically adjusts to perfectly fit the longest track within the visible workspace.
• Eliminates the need for horizontal scrolling to see the entire project length.

User Value:

• Significantly improves UX efficiency, especially for long-form video editing.
• Provides a quick, one-click overview of the entire project layout.