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.ts

@@ -193,15 +193,19 @@ function persistOptimistic(path: string, content: string, onFail: (p: string) =>
   persistNewNote(path, content).catch(() => onFail(path))
 }
 
-/** Optimistically add entry to UI, open tab, and persist to disk. */
+/** Optimistically open tab, add entry to vault, and persist to disk.
+ *  Tab creation (setTabs/setActiveTabPath) runs at normal priority so the
+ *  tab appears instantly.  addEntry uses startTransition internally so the
+ *  expensive entries update (NoteList re-filter/sort on 9000+ entries) is
+ *  deferred and doesn't block the tab from rendering. */
 function createAndPersist(
   resolved: { entry: VaultEntry; content: string },
   addFn: (e: VaultEntry, c: string) => void,
   openTab: (e: VaultEntry, c: string) => void,
   onFail: (p: string) => void,
 ): void {
-  addEntryWithMock(resolved.entry, resolved.content, addFn)
   openTab(resolved.entry, resolved.content)
+  addEntryWithMock(resolved.entry, resolved.content, addFn)
   persistOptimistic(resolved.entry.path, resolved.content, onFail)
 }