* fix(dashboard): comprehensive dark mode improvements for WebUI
- Tune DarkTheme.ts color palette: soften primary, fix on-surface-variant
from black to light grey, adjust surface/background/border colors,
add codeBg/preBg/code variables for dark code blocks
- Add _HljsDark.scss for highlight.js dark token overrides and
markstream-vue CSS variable overrides under .v-theme--PurpleThemeDark
- Add global dark mode overrides in _override.scss: soften flat primary
buttons, timeline dots, dialog card backgrounds, markdown link color
- Fix hardcoded light backgrounds in IPythonToolBlock, ExtensionCard,
T2ITemplateEditor, ExtensionPage, KnowledgeBase, LongTermMemory
- Remove hardcoded color='black' from icons in ProviderPage,
PlatformPage, PersonaPage
- Desaturate console log ANSI colors for dark mode readability
- Add iframe dark mode inversion filter in VerticalSidebar
- Fix language switcher mobile adaptation and click behavior
- Fix login page theme toggle tooltip showing wrong label
* fix(dashboard): apply dark mode review feedback
* fix: update scrollbar styles to follow theme variables
* fix: update theme colors to use CSS variables for consistency
* fix: change login button color to primary for better visibility
* fix: update theme colors for Dark and Light themes; change login button color to secondary
* fix: update border and theme colors for consistency in DarkTheme
* fix: update sidebar list class to conditionally hide scrollbar in mini sidebar mode
* fix: simplify button visibility logic and remove unnecessary leftPadding style
* fix: refactor language switcher to use grouped menu for better UX
* fix: update theme colors to use primary color for consistency across components
* fix: add preview text for template output in multiple languages