fix: defer vault entries update via startTransition for instant tab creation (#90)

On a 9000+ entry vault, creating a new note (Cmd+N) was slow because
the entries state update triggered expensive re-computations in NoteList
(filter + sort), Sidebar (type counts), and Editor (wikilink suggestions)
— all blocking the tab from appearing.

Fix: wrap setEntries/setAllContent/trackNew in React's startTransition so
they run as low-priority updates. The tab creation (setTabs/setActiveTabPath)
remains high-priority and renders in <50ms. The entries update is deferred
to idle time without blocking the UI.

Also reorder createAndPersist to call openTab before addEntry, making the
intent explicit: tab appears first, vault index updates second.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useNoteActions.test.ts

@@ -312,6 +312,24 @@ describe('useNoteActions hook', () => {
     expect(createdContent).toContain('title: Test Note')
   })
 
+  it('handleCreateNote opens tab immediately (before addEntry resolves)', () => {
+    const callOrder: string[] = []
+    const trackedAddEntry = vi.fn(() => { callOrder.push('addEntry') })
+    const config = makeConfig()
+    config.addEntry = trackedAddEntry
+
+    const { result } = renderHook(() => useNoteActions(config))
+
+    act(() => {
+      result.current.handleCreateNote('Fast Note', 'Note')
+    })
+
+    // Tab should be open with the new note
+    expect(result.current.tabs).toHaveLength(1)
+    expect(result.current.tabs[0].entry.title).toBe('Fast Note')
+    expect(result.current.activeTabPath).toContain('note/fast-note.md')
+  })
+
   it('handleCreateType creates type entry', () => {
     const { result } = renderHook(() => useNoteActions(makeConfig()))