Add viewer database import and clarify backup actions.

Pairs export with validated .db restore, documents the difference from game
save imports, and renames the JSON upload button to Import game backup.

Co-authored-by: Cursor <cursoragent@cursor.com>

static/app.js

@@ -74,6 +74,7 @@ async function init() {
   setupNav();
   setupUpload();
   setupExport();
+  setupViewerDbImport();
   setupGlobalSearch();
   setupGoalModal();
   await loadData();
@@ -163,9 +164,47 @@ function setupExport() {
   const el = document.getElementById("export-viewer");
   if (!el) return;
   el.href = `${apiBase()}/export`;
+  el.title = t("viewerDb.exportHint");
   el.addEventListener("click", () => trackEvent("Viewer Export"));
 }
 
+function setupViewerDbImport() {
+  const input = document.getElementById("viewer-db-upload");
+  if (!input) return;
+  input.addEventListener("change", async (e) => {
+    const file = e.target.files[0];
+    e.target.value = "";
+    if (!file) return;
+    if (!file.name.toLowerCase().endsWith(".db")) {
+      alert(t("viewerDb.invalidFile"));
+      return;
+    }
+    if (!confirm(t("viewerDb.importConfirm"))) return;
+
+    const fd = new FormData();
+    fd.append("file", file);
+    const res = await fetch(`${apiBase()}/import-viewer`, { method: "POST", body: fd });
+    const result = await res.json();
+    if (!res.ok || result.error) {
+      alert(result.error || t("viewerDb.importFailed"));
+      return;
+    }
+
+    trackEvent("Viewer Import", {
+      snapshots: String(result.snapshots || 0),
+      goals: String(result.goals || 0),
+    });
+    state.lastImportChanges = null;
+    state.inventoryTimeline = null;
+    state.skillTimeline = null;
+    await loadData();
+    alert(t("viewerDb.importSuccess", {
+      snapshots: result.snapshots || 0,
+      goals: result.goals || 0,
+    }));
+  });
+}
+
 function setupGlobalSearch() {
   const input = document.getElementById("global-search");
   if (!input) return;