Fix/agentflow Fixed theming for dark mode in agentflow

[j-sanaa]

1. Fixed background color of Input fields

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2. Fixed border for Messages/Tools input
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3. Fixed border color for Accordion
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4. Fixed node editing background color
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[gemini-code-assist]

Code Review

This pull request implements dark mode improvements across various UI components by replacing hardcoded colors with theme-aware tokens and the divider palette color. It also updates the theme configuration and token definitions. Feedback includes addressing hardcoded text colors in RichTextEditor and VariableInput that may cause visibility issues in dark mode, simplifying redundant styles in the theme configuration, and avoiding the use of 'as any' in unrelated logic changes.