🎨 Palette: [UX improvement] Add tooltips to custom icon-only interactive widgets

[JustLookAtNow]

💡 What:

Added Tooltip wrappers to custom icon-only interactive components that use GestureDetector. Specifically:

1. The "expand tags" down-arrow button in lib/widgets/torrent_list_item.dart.
2. The site color picker circle in lib/pages/server_settings_page.dart.

🎯 Why:

While standard IconButton widgets accept a tooltip property, custom interactive icons built using GestureDetector or InkWell do not. This leaves these elements completely inaccessible to screen readers and prevents helpful hover text from displaying on desktop and web environments.

♿ Accessibility:

• Screen readers will now correctly announce "展开标签" (Expand tags) and "选择站点颜色" (Select site color) instead of silence or a generic "button" label.
• Mouse and hover interactions on desktop/web will now present descriptive text, aiding discoverability.

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PR created automatically by Jules for task 16915671100134482092 started by @JustLookAtNow

[google-labs-jules]

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