fix: customize icon & color works for types without Type entry (#173)

Types without a dedicated Type definition note in the vault silently
failed to save icon/color customizations. Both applyCustomization
(Sidebar) and handleCustomizeType (useEntryActions) returned early
when no Type entry existed. Also fixed a race condition where two
concurrent handleUpdateFrontmatter calls could overwrite each other.

Changes:
- useNoteActions: add createTypeEntrySilent for headless Type file creation
- useEntryActions: auto-create Type entry when missing, serialize writes
- Sidebar: applyCustomization proceeds with defaults when no Type entry
- App: wire createTypeEntrySilent into useEntryActions config

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

src/components/Sidebar.tsx

@@ -151,8 +151,9 @@ function applyCustomization(
 ): void {
   if (!target || !onCustomizeType) return
   const te = typeEntryMap[target]
-  if (!te) return
-  const [icon, color] = buildCustomizeArgs(te, prop, value)
+  const [icon, color] = te
+    ? buildCustomizeArgs(te, prop, value)
+    : [prop === 'icon' ? value : 'file-text', prop === 'color' ? value : 'blue']
   onCustomizeType(target, icon, color)
 }