[UI Design] Optimize the function feedback interface

[wenjiangping]

Related: #3390

Background

The feedback flow in #3390 is functionally complete but still needs UI and interaction refinement to make feedback submission and notification handling clearer and easier to use.

Goal

Improve the feedback form, submission states, attachment presentation, and notification center so users can understand and complete the feedback flow more easily.

Proposed approach

Simplify the layout and interaction flow, clarify required fields and status feedback, and improve the presentation of notifications, replies, and image previews.

Acceptance criteria

• The feedback form and notification center have a clear, consistent, and easy-to-understand layout.
• The optimized UI works on supported desktop and narrow-screen layouts without breaking existing functionality.