Previously, Tab only handled dropdown completions. Users seeing gray
ghost text from history-based suggestions had no way to accept them
with Tab - they had to use Right arrow or Ctrl+E.
Now Tab follows priority:
1. Completion menu open → accept selected completion
2. Ghost text suggestion available → accept auto-suggestion
3. Otherwise → start completion menu
This matches user intuition that Tab should 'complete what I see.'
StefanIsMe