feat: replace tray Show button with Settings and About entries

[StudentWeis]

Motivation

The tray menu previously only had "Show" and "Quit" options. Users want direct access to Settings and About pages from the tray without going through the main clipboard list first.

Proposed Solution

• Remove the "Show" menu item from the system tray.
• Add "Settings" and "About" menu items that open the window directly to the corresponding panel.
• Left-clicking the tray icon opens Settings directly.
• Add an activated flag so the initial hidden window renders an empty background instead of the clipboard list, preventing a flash of the wrong content on first activation.

Alternatives Considered

• Keeping "Show" and adding Settings/About alongside: rejected because it clutters the tray menu and "Show" is redundant when the user can left-click.

Acceptance Criteria

• Tray menu shows "Settings", "About", and "Quit" (no "Show")
• Clicking "Settings" opens the window directly to the Settings panel
• Clicking "About" opens the window directly to the About panel
• Left-clicking the tray icon opens the Settings panel
• No flash of the clipboard list on first activation
• All locale files updated (en, zh-CN, ja)
• All existing tray tests pass

Scope

gui