refactor(chat): remove dead syntaxTheme plumbing

The Prism syntaxTheme prop is no longer read after code highlighting moved to
the Shiki worker. Remove the now-dead prop threading and its source.

- Drop syntaxTheme from interfaces, destructures, prop passes, and React.memo
  comparators across ChatMessage, MessageBody, ProgressiveGroup, ToolPart,
  TurnActivity, ToolOutputDialog, and ChatInput.
- Drop the unused _syntaxTheme param from renderWebSearchOutput.
- Remove the dead generateSyntaxTheme usages (ChatMessage memo, PlanView
  unassigned memo) and delete the now-unimported syntaxThemeGenerator module.

packages/ui/src/lib/theme/syntaxThemeGenerator.ts

@@ -1,208 +0,0 @@
-import type { Theme } from '@/types/theme';
-
-export function generateSyntaxTheme(theme: Theme) {
-  const syntax = theme.colors.syntax;
-  const surface = theme.colors.surface;
-
-  return {
-    'code[class*="language-"]': {
-      color: syntax.base.foreground,
-      background: 'transparent',
-      fontFamily: 'Consolas, Monaco, "Andale Mono", "Ubuntu Mono", monospace',
-      fontSize: '1em',
-      textAlign: 'left' as const,
-      whiteSpace: 'pre',
-      wordSpacing: 'normal',
-      wordBreak: 'normal' as const,
-      wordWrap: 'normal' as const,
-      lineHeight: '1.5',
-      MozTabSize: '4',
-      OTabSize: '4',
-      tabSize: '4',
-      WebkitHyphens: 'none' as const,
-      MozHyphens: 'none' as const,
-      msHyphens: 'none' as const,
-      hyphens: 'none' as const,
-    },
-    'pre[class*="language-"]': {
-      color: syntax.base.foreground,
-      background: 'transparent',
-      fontFamily: 'Consolas, Monaco, "Andale Mono", "Ubuntu Mono", monospace',
-      fontSize: '1em',
-      textAlign: 'left' as const,
-      whiteSpace: 'pre',
-      wordSpacing: 'normal',
-      wordBreak: 'normal' as const,
-      wordWrap: 'normal' as const,
-      lineHeight: '1.5',
-      MozTabSize: '4',
-      OTabSize: '4',
-      tabSize: '4',
-      WebkitHyphens: 'none' as const,
-      MozHyphens: 'none' as const,
-      msHyphens: 'none' as const,
-      hyphens: 'none' as const,
-      padding: '0',
-      margin: '0',
-      overflow: 'auto',
-    },
-
-    comment: {
-      color: syntax.base.comment,
-      fontStyle: 'italic',
-    },
-    prolog: {
-      color: syntax.base.comment,
-    },
-    doctype: {
-      color: syntax.base.comment,
-    },
-    cdata: {
-      color: syntax.base.comment,
-    },
-
-    punctuation: {
-      color: syntax.tokens?.punctuation || surface.mutedForeground,
-    },
-
-    property: {
-      color: syntax.tokens?.variableProperty || syntax.base.variable,
-    },
-    tag: {
-      color: syntax.tokens?.tag || syntax.base.keyword,
-    },
-    'attr-name': {
-      color: syntax.tokens?.tagAttribute || syntax.base.variable,
-    },
-    'attr-value': {
-      color: syntax.tokens?.tagAttributeValue || syntax.base.string,
-    },
-
-    boolean: {
-      color: syntax.tokens?.boolean || syntax.base.number,
-    },
-    number: {
-      color: syntax.base.number,
-    },
-    constant: {
-      color: syntax.tokens?.constant || syntax.base.number,
-    },
-    symbol: {
-      color: syntax.tokens?.constant || syntax.base.number,
-    },
-
-    string: {
-      color: syntax.base.string,
-    },
-    char: {
-      color: syntax.base.string,
-    },
-
-    function: {
-      color: syntax.base.function,
-    },
-    builtin: {
-      color: syntax.tokens?.functionBuiltin || syntax.base.function,
-    },
-
-    'class-name': {
-      color: syntax.tokens?.className || syntax.base.type,
-    },
-    namespace: {
-      color: syntax.tokens?.namespace || syntax.base.type,
-      opacity: 0.8,
-    },
-
-    keyword: {
-      color: syntax.base.keyword,
-    },
-    atrule: {
-      color: syntax.base.keyword,
-    },
-    selector: {
-      color: syntax.base.function,
-    },
-
-    operator: {
-      color: syntax.base.operator,
-    },
-
-    variable: {
-      color: syntax.base.variable,
-    },
-
-    regex: {
-      color: syntax.tokens?.regex || syntax.base.string,
-    },
-
-    url: {
-      color: syntax.base.function,
-      textDecoration: 'underline',
-    },
-    entity: {
-      color: syntax.base.function,
-      cursor: 'help',
-    },
-
-    '.language-css .token.string': {
-      color: syntax.base.string,
-    },
-    '.style .token.string': {
-      color: syntax.base.string,
-    },
-
-    deleted: {
-      color: theme.colors.status.error,
-      backgroundColor: theme.colors.status.errorBackground,
-    },
-    inserted: {
-      color: theme.colors.status.success,
-      backgroundColor: theme.colors.status.successBackground,
-    },
-
-    title: {
-      color: theme.colors.primary.base,
-      fontWeight: 'bold',
-    },
-    'code-block': {
-      color: syntax.base.string,
-    },
-    'code-snippet': {
-      color: syntax.base.string,
-    },
-    list: {
-      color: syntax.base.variable,
-    },
-    hr: {
-      color: surface.mutedForeground,
-    },
-    table: {
-      color: syntax.base.function,
-    },
-    blockquote: {
-      color: surface.mutedForeground,
-      fontStyle: 'italic',
-    },
-
-    important: {
-      color: syntax.base.keyword,
-      fontWeight: 'bold',
-    },
-    bold: {
-      fontWeight: 'bold',
-    },
-    italic: {
-      fontStyle: 'italic',
-    },
-    strike: {
-      textDecoration: 'line-through',
-    },
-
-    decorator: {
-      color: syntax.tokens?.decorator || syntax.base.function,
-    },
-    annotation: {
-      color: syntax.tokens?.decorator || syntax.base.function,
-    },
-  };
-}