feat(calendar): remember .pst path, add auto-sync-on-launch toggle

Prefills the file path from settings once loaded (without clobbering
an in-progress browse/edit) and persists it after a successful import,
so the user doesn't have to re-browse to the same file every launch.
The new checkbox just flips pst_auto_sync, which lib.rs's one-shot
startup pass reads.

src/lib/views/Settings.svelte

@@ -194,6 +194,14 @@
     }),
   );
 
+  // Prefills the remembered path once settings load, without clobbering
+  // whatever the user is actively typing/browsing to.
+  $effect(() => {
+    if (!pstPath && settings.settings.pst_last_path) {
+      pstPath = settings.settings.pst_last_path;
+    }
+  });
+
   async function pickPstFile() {
     const path = await open({ filters: [{ name: "Outlook data file", extensions: ["pst"] }] });
     if (typeof path === "string") pstPath = path;
@@ -202,6 +210,10 @@
     if (!pstPath) return;
     await calendar.importPst(pstPath, pstPassword || undefined);
     pstPassword = "";
+    if (!calendar.importError) await settings.patch({ pst_last_path: pstPath });
+  }
+  function onToggleAutoSync(e: Event) {
+    settings.patch({ pst_auto_sync: (e.target as HTMLInputElement).checked });
   }
   function formatEventDate(unixSecs: number | null): string {
     if (!unixSecs) return "";
@@ -717,6 +729,18 @@
             >
           {/if}
         </div>
+        <label class="row">
+          <input
+            type="checkbox"
+            checked={settings.settings.pst_auto_sync}
+            onchange={onToggleAutoSync}
+          />
+          <span>Re-import this file automatically on launch</span>
+        </label>
+        <p class="muted small">
+          Runs once at startup, not on a timer — re-import is safe to repeat (existing events are
+          matched and updated, not duplicated).
+        </p>
         {#if calendar.importError}
           <p class="error">
             Import failed: {calendar.importError} — the file itself is untouched; check the path and try