feat: adding color theme mode setting

[ACTCD]

resolve

• Light theme for the UI of the extension itself #392 (comment)
• part of Custom extension color scheme #777

[ACTCD]

It does not take effect on the iOS settings page. Will solve it in the future.

[ACTCD]

There are some upstream bugs that are known to exist in different system versions, for example:

• Click any extension button and Safari will ignore the color-scheme css of the Editor page, until reload.
• Safari may ignore popup's child element color-scheme override, the specific mechanism is unknown.

These should not be considered implementation issues for this extension and can only wait for upstream fixes.

[ACTCD]

Since the current settings changes are persisted async and do not await for completion, if the user closes the page too quickly, the settings may not be persisted, although this is usually not happens.

But later refactoring should probably add indicators and await for persistence to complete.