split boot() into initSettings/initDataAndEngine/initUI

Boot had grown into one long function covering settings load, engine
and workspace setup, and all the UI wiring. Split along those natural
phase boundaries; boot() itself is now just the three awaits in order.

src/main.ts

@@ -700,13 +700,19 @@ function toast(msg: string): void {
 
 // ---------- boot
 
-async function boot(): Promise<void> {
+async function initSettings(): Promise<void> {
   settings = await loadSettings();
   if (!localStorage.getItem("summarum.langInit") && settings.language === "en") {
     settings.language = detectLang();
     localStorage.setItem("summarum.langInit", "1");
   }
 
+  // snapshots run before the app writes anything
+  setDataDir(settings.dataDir);
+  await runBackups(settings.dataDir, settings.deletedRetentionDays);
+}
+
+async function initDataAndEngine(): Promise<void> {
   engine = new SumEngine({
     precision: settings.precision,
     groupSeparator: settings.groupSeparator,
@@ -714,10 +720,6 @@ async function boot(): Promise<void> {
     dateFormat: settings.dateFormat,
   });
 
-  // snapshots run before the app writes anything
-  setDataDir(settings.dataDir);
-  await runBackups(settings.dataDir, settings.deletedRetentionDays);
-
   const stored = await loadAppData(settings.dataDir);
   // a corrupt or foreign documents.json must not crash the boot
   if (stored && Array.isArray(stored.docs) && stored.docs.length > 0 && stored.contents && typeof stored.contents === "object") {
@@ -782,6 +784,9 @@ async function boot(): Promise<void> {
       editor.goToLine(line);
     },
   });
+}
+
+async function initUI(): Promise<void> {
 
   applySettings(); // sets the language before bindSettingsUI renders dynamic labels
   bindSettingsUI();
@@ -981,6 +986,12 @@ async function boot(): Promise<void> {
   setInterval(() => { if (settings.autoUpdateEnabled) void checkUpdate(); }, 6 * 60 * 60 * 1000);
 }
 
+async function boot(): Promise<void> {
+  await initSettings();
+  await initDataAndEngine();
+  await initUI();
+}
+
 /** manual = true when the user clicked "Check for updates" — only then report "up to date" / "check failed" */
 async function checkUpdate(manual = false): Promise<void> {
   const result = await checkForUpdate();