Merge #502: read-only XLSX spreadsheet preview in the file-preview overlay

# Conflicts:
#	CLAUDE.md

config/test-suites.ts

@@ -41,6 +41,7 @@ export const BROWSER_TEST_GLOBS = [
   'test/git-status.browser.test.ts',
   'test/split-pane-orchestration.browser.test.ts',
   'test/split-pane-auto-collapse.browser.test.ts',
+  'test/spreadsheet-preview.browser.test.ts',
   'test/mobile-ime-preview.browser.test.ts',
   'test/run-mode-menu-scroll.browser.test.ts',
 ];