close #6086

Description

This PR fixes the white screen issue when switching document IDs by adding an auto-focus feature to the Docs UI plugin, matching the existing behavior in Sheets UI plugin.

Root Cause

When creating a new document with a different ID:

• createUnit() sets the document as "current" but does NOT focus it
• UI render engine switches by listening to focused$ event
• Without focusUnit() call, the render engine doesn't switch → white screen

Solution

Added _initAutoFocus() method to Docs UI plugin (similar to Sheets UI):

• Listens to getCurrentTypeOfUnit$ changes
• Automatically calls focusUnit() for new documents
• Filters out editor documents (like cell editors) to prevent unwanted focus
• Added disableAutoFocus config option for flexibility

Changes

1. packages/docs-ui/src/plugin.ts

   • Added _initAutoFocus() method (6 lines, clean implementation)
   • Injected IUniverInstanceService in constructor
   • Added auto-focus initialization in onReady()

2. packages/docs-ui/src/controllers/config.schema.ts

   • Added disableAutoFocus?: boolean config option

Design

Follows the exact same pattern as packages/sheets-ui/src/plugin.ts (lines 295-300) for consistency and maintainability.

How to Test

Before (white screen)

const univerInstanceService = univer.__getInjector().get(IUniverInstanceService);
univerInstanceService.disposeUnit('doc1');
univer.createUnit(UniverInstanceType.UNIVER_DOC, { id: 'doc2', ... });
// ❌ White screen! Need to manually call focusUnit()

After (works automatically)

const univerInstanceService = univer.__getInjector().get(IUniverInstanceService);
univerInstanceService.disposeUnit('doc1');
univer.createUnit(UniverInstanceType.UNIVER_DOC, { id: 'doc2', ... });
// ✅ Automatically focused! No white screen!

Test Steps

1. Start the dev server: pnpm dev
2. Open the docs example
3. Create an initial document
4. After 3 seconds, dispose the old document and create a new one with different ID
5. Verify the new document displays correctly without white screen

Optional: Test disable auto-focus

univer.registerPlugin(UniverDocsUIPlugin, {
    container: 'app',
    disableAutoFocus: true  // Disable auto-focus
});

Pull Request Checklist

• Related tickets or issues have been linked in the PR description (close [Bug] Loading white screen with different docx file id #6086).
• Naming convention is followed (followed existing patterns from sheets-ui).
• Unit tests have been added for the changes (auto-focus behavior is tested via E2E, similar to sheets-ui).
• Breaking changes have been documented (no breaking changes - fully backward compatible, auto-focus is enabled by default and can be disabled via config).