desktop: Import and Export work offline; the menu toggle is reachable; errors say why

Export and Import were a link to the server and a reject("needs a server") on the
desktop. Both now run in the core with no server:

- core/src/local/portable.rs builds the same zip the server writes (notes.json,
  a Markdown file per note, each attachment this device holds) and reads either
  export marker or a Google Keep Takeout zip, with the server's decompression
  budget and an all-or-nothing transaction. Export saves to Downloads (no new
  plugin) and the sidebar says where; Import takes the archive as raw IPC bytes.
- core/testdata/portable.json pins the format for both copies: the server runs
  its Keep and native readers against it (test_portable_fixture.py) and checks
  its real export's keys (test_integration.py); the core runs the same cases.
- Found on the way: both importers skipped a Keep note that is only a photo as
  "empty". It now imports, on the server and in the core.
- New dependency, approved: `zip` (deflate only) plus `flate2` on its pure-Rust
  backend, both already in the lockfile.

The AppImage applications-menu toggle moves from Account, which the desktop
never shows, to the Sync page; the first-run prompt now says so.

errorMessage (#5236) replaces the hand-rolled `.error ?? …` / `.message ?? e`
reads at the remaining catch sites, so a desktop failure shows its real reason.

Task #5170.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/views/AccountView.vue

@@ -7,7 +7,7 @@ import BaseButton from "../components/BaseButton.vue";
 import BaseInput from "../components/BaseInput.vue";
 import ClientDownloads from "../components/ClientDownloads.vue";
 import Icon from "../components/Icon.vue";
-import { isDesktop, desktop as desktopBridge, type IntegrationStatus } from "../desktop/bridge";
+import { errorMessage } from "../api/errors";
 
 // Per-user (not admin) management of linked native clients — the Tauri desktop and
 // Android apps authenticate sync with a device bearer token issued here.
@@ -23,9 +23,6 @@ const creating = ref(false);
 // The freshly-issued plaintext token — shown ONCE (never retrievable again).
 const freshToken = ref("");
 
-// Desktop-app self-integration (Linux AppImage only; the card is hidden otherwise).
-const desktopStatus = ref<IntegrationStatus | null>(null);
-const desktopBusy = ref(false);
 
 async function load() {
   error.value = "";
@@ -45,7 +42,7 @@ async function link() {
     freshToken.value = await devices.create(newName.value.trim() || "Device");
     newName.value = "";
   } catch (e) {
-    error.value = (e as { error?: string }).error ?? "Couldn't create a device token.";
+    error.value = errorMessage(e, "Couldn't create a device token.");
   } finally {
     creating.value = false;
   }
@@ -74,36 +71,8 @@ function fmt(iso: string | null): string {
   return new Date(iso).toLocaleString();
 }
 
-async function loadDesktop() {
-  if (!isDesktop()) return;
-  try {
-    desktopStatus.value = await desktopBridge.integrationStatus();
-  } catch {
-    desktopStatus.value = null;
-  }
-}
-
-async function toggleIntegration() {
-  desktopBusy.value = true;
-  try {
-    desktopStatus.value = desktopStatus.value?.is_integrated
-      ? await desktopBridge.unintegrate()
-      : await desktopBridge.integrate();
-    ui.showToast(
-      desktopStatus.value?.is_integrated
-        ? "Added to your applications menu."
-        : "Removed from your applications menu.",
-    );
-  } catch (e) {
-    ui.showToast((e as { message?: string }).message ?? "Couldn't update the menu entry.");
-  } finally {
-    desktopBusy.value = false;
-  }
-}
-
 onMounted(() => {
   void load();
-  void loadDesktop();
 });
 </script>
 
@@ -132,31 +101,6 @@ onMounted(() => {
       paste it into the app when it asks to connect. You can revoke a device at any time.
     </p>
 
-    <!-- Desktop app self-integration (Linux AppImage only) -->
-    <section
-      v-if="desktopStatus?.is_appimage"
-      class="mb-6 flex items-center justify-between gap-4 rounded-xl border border-neutral-200 p-4 dark:border-neutral-800"
-    >
-      <div class="min-w-0">
-        <p class="text-sm font-medium text-neutral-800 dark:text-neutral-100">Desktop app</p>
-        <p class="mt-0.5 text-xs text-neutral-400">
-          {{
-            desktopStatus.is_integrated
-              ? "Inkwell is in your applications menu."
-              : "Add Inkwell to your applications menu to launch it like an installed app."
-          }}
-        </p>
-      </div>
-      <BaseButton
-        :variant="desktopStatus.is_integrated ? 'ghost' : 'primary'"
-        :loading="desktopBusy"
-        class="shrink-0"
-        @click="toggleIntegration"
-      >
-        {{ desktopStatus.is_integrated ? "Remove" : "Add to applications" }}
-      </BaseButton>
-    </section>
-
     <!-- Every client this server holds, the one that fits this machine on top.
          Hides itself when the server holds none. -->
     <ClientDownloads />