Optimizing widgets style and visual

[Lori-Shu]

No description provided.

[pullfrog]

✅ No new issues found.

Reviewed changes — this PR optimizes the UI style and visuals of the widgets, including updated color schemes, added styling for the control bar, and a timeout for subtitle display.

• Updated AppUI visuals — adjusted window and panel colors for a consistent look.
• Improved ControlbarUI styling — wrapped the control bar in a styled frame with shadows and updated slider styling.
• Added subtitle timeout — subtitles now disappear after 2 seconds.
• Cleaned up debug logs — removed "debug point" log statements in whispercpp_transcriber.

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