feat(editor): Shiki syntax highlighting in the file editor (CodeMirror)

Bring the CodeMirror file editor up to the same rich highlighting as the Shiki
file view, so toggling edit <-> view is visually consistent. lezer collapses far
more tokens than TextMate (import/from/const are all "keyword"), so a theme
remap can't reach parity — instead, project real Shiki tokens onto decorations.

- Worker: add highlightTokens — tokenize with an arbitrary registered TextMate
  theme and return per-line styled runs with offsets. The theme object ships to
  the worker once per name; later calls send only the name.
- New shikiHighlight CodeMirror extension: a StateField of mark decorations
  built from worker tokens. Re-tokenizes on a short idle (off the keystroke
  path) and maps decorations through edits so colors persist while typing.
- flexokiTheme: add { syntaxColors: false } to keep only the editor UI theme,
  so the lezer highlighter doesn't compete with the Shiki decorations.
- FilesView: enable Shiki highlighting (same language resolver as the file view
  → identical language) and drop lezer token colors when it's active. lezer
  language stays on for indentation/folding/brackets.

packages/ui/src/lib/codemirror/flexokiTheme.ts

@@ -6,7 +6,13 @@ import { classHighlighter, tags as t } from '@lezer/highlight';
 
 import type { Theme } from '@/types/theme';
 
-export function createFlexokiCodeMirrorTheme(theme: Theme): Extension {
+export function createFlexokiCodeMirrorTheme(
+  theme: Theme,
+  // When syntax colors are provided elsewhere (e.g. the Shiki decoration
+  // extension), pass `{ syntaxColors: false }` to keep only the editor UI theme
+  // (gutters, selection, cursor) and avoid a competing token color source.
+  options?: { syntaxColors?: boolean },
+): Extension {
   const isDark = theme.metadata.variant === 'dark';
 
   const monoFont = theme.config?.fonts?.mono || 'monospace';
@@ -554,6 +560,10 @@ export function createFlexokiCodeMirrorTheme(theme: Theme): Extension {
     },
   ]);
 
+  if (options?.syntaxColors === false) {
+    return [ui];
+  }
+
   return [
     ui,
     syntaxHighlighting(defaultHighlightStyle, { fallback: true }),