Fix: New tab opens with scroll position not at top

[malibio]

Problem

When opening a new tab to view a root node, the scroll position is not at the top of the document. Users have to manually scroll up to see the beginning of the content.

Root Cause Analysis

The issue is caused by element.focus() calls in the cursor positioning system that don't use { preventScroll: true }. When the browser focuses an element that's below the visible viewport, it automatically scrolls to make it visible.

Key files involved:

• packages/desktop-app/src/lib/design/components/textarea-controller.svelte.ts - focus() method at line ~434
• packages/desktop-app/src/lib/services/cursor-positioning-service.ts - multiple textarea.focus() calls

Proposed Solution

Add { preventScroll: true } to focus calls, but this needs careful manual testing because:

1. Our unit tests use mocked DOM and don't detect real browser focus/scroll behavior
2. Cursor positioning has broken multiple times in the past without test detection
3. The change affects all focus operations (Enter key, arrow navigation, node creation, etc.)

Testing Requirements

Before implementing, manually test these scenarios:

• Enter key creates new node - cursor should be in new node
• Arrow up/down navigation between nodes
• Clicking on a node to edit
• Creating a node via slash command
• Tab switching preserves scroll position
• New tab opens at scroll top
• Indent/outdent operations
• Node type conversion (text → task, etc.)

Related

• Scroll state management: packages/desktop-app/src/lib/stores/scroll-state.ts
• Base node viewer scroll restoration: base-node-viewer.svelte lines 323-334

[malibio]

Test baseline: Frontend 3501 passed (104 files), Rust 751 passed, 2 pre-existing failures (test_add_to_collection_assigns_order, test_node_service_idempotent_seeding)