[mkroemer]

Builds on #4 (theming). Until that is merged this PR shows its commit too; the icons part is the last three commits.

This lets a host draw the viewer's chrome with its own icon set, all of it or just a few icons.

Every icon the chrome draws now goes through Icon. A few controls still used text glyphs: the zoom buttons, the outline toggle and its close button, find & replace, Present and the add-sheet tab. They get the names zoomIn, zoomOut, present, sheetAdd and replace (outline and close are reused) and look the same as before.

icons on DocViewer, mount() and <office-viewer> (as the .icons property) takes a partial map or a resolver:

<DocViewer src={file} icons={{ undo: <MyUndo />, redo: <MyRedo /> }} />

const lucide = (name: IconName) => {
  const C = LUCIDE[name]
  return C && <C size="1em" strokeWidth={1.8} />
}
<DocViewer src={file} icons={lucide} />

A name the map leaves out, or a resolver returning undefined or null, keeps the built-in icon. Host icons render in span.de-icon, sized by its font-size, so an icon drawn at 1em with currentColor follows the size and the theme. IconName is the union of the built-in names (all of them in ICON_NAMES), and the icon props in the toolbars, menus and FileMenuItem are typed with it. IconsProvider gives the standalone views the same icons; a nested provider falls back to the enclosing one. docs/api.md has Lucide and Phosphor examples; there are no new dependencies.

test/icons.test.tsx covers the precedence of map, resolver and built-in icons. e2e/icons.spec.ts checks that host icons replace the built-in ones in the DOCX, XLSX and PPTX chrome. bun run typecheck, bun test and the e2e suite pass in CI.

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