Fix: Switch the default theme from light mode to dark mode and improve some styles #9869 (#10552)

### What problem does this PR solve?

Fix: Switch the default theme from light mode to dark mode and improve
some styles #9869
-Update UI component styles such as input boxes, tables, and prompt
boxes
-Optimize login page layout and style details
-Revise some of the wording, such as uniformly changing "data flow" to
"pipeline"
-Adjust the parser to support the markdown type

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/components/theme-provider.tsx

@@ -21,7 +21,7 @@ const ThemeProviderContext = createContext<ThemeProviderState>(initialState);
 
 export function ThemeProvider({
   children,
-  defaultTheme = ThemeEnum.Light,
+  defaultTheme = ThemeEnum.Dark,
   storageKey = 'vite-ui-theme',
   ...props
 }: ThemeProviderProps) {