Add built-in auto-updater with tab-bar update pill

Wires electrobun's Updater to the /dl download host. The packaged app checks
https://miniscp.com/dl on launch + every 6h; when a newer build exists, an
accent-colored "update tool" appears next to Connections in the tab bar. It
announces the update, becomes its own inline progress bar while downloading,
then flips to "Restart to apply" (two-step: download, then user-triggered
relaunch).

- electrobun.config.ts: release.baseUrl = https://miniscp.com/dl (baked into
  version.json at build; miniscp.com fronted by an external proxy for TLS).
- rpc.ts: checkForUpdate/downloadUpdate/applyUpdate requests + updateStatus push.
- rpc-handlers.ts + index.ts: call Updater; poll on launch+6h; stream
  onStatusChange progress. checkForUpdate self-guards the dev channel.
- rpc.service.ts + new updater.service.ts: signal-based state
  (available -> downloading -> ready, ready derived from downloadUpdate ok).
- tab-bar.ts: single bg-primary pill; progress fills the pill itself.
- icons.ts: register mynaDownload. i18n: tabBar + menu keys across all locales.
- menu.ts + app.ts: "Check for Updates…" app-menu item -> UpdaterService.check().
- docs: build-and-release + architecture updated.

Unsigned builds still update (applyUpdate strips the macOS quarantine xattr).
Verified: tsc --noEmit (exit 0) + build:ui AOT (exit 0). Live pill + full
download/apply flow require a two-build test on the host.

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

ui/src/app/tab-bar/tab-bar.ts

@@ -8,6 +8,7 @@ import { PanelsService } from '../panels.service';
 import { IS_MAC_CHROME, MOD_LABEL } from '../platform';
 import { RpcService } from '../rpc.service';
 import { SettingsService } from '../settings.service';
+import { UpdaterService } from '../updater.service';
 
 const THEMES = ['system', 'light', 'dark'] as const;
 const DARK_TONES = ['dark', 'darker'] as const;
@@ -105,6 +106,37 @@ const CONCURRENCY_CHOICES = [2, 3, 4, 6, 8] as const;
 
       <div class="flex-1"></div>
 
+      <!-- auto-update tool: one accent pill that announces the update, becomes its
+           own progress bar while downloading, then turns into "Restart to apply" -->
+      @if (updater.state() !== 'idle' && updater.state() !== 'error') {
+        <button
+          (click)="onUpdateClick()"
+          [disabled]="updater.state() === 'downloading'"
+          [title]="i18n.t('tabBar.updateTooltip', { version: updater.version() })"
+          class="relative mr-1 grid h-6 place-items-center overflow-hidden rounded-md px-2.5 text-[11px] font-medium bg-primary text-primary-foreground electrobun-webkit-app-region-no-drag hover:opacity-90 disabled:cursor-default"
+        >
+          @if (updater.state() === 'downloading') {
+            <span
+              class="absolute inset-y-0 left-0 bg-primary-foreground/25 transition-[width] duration-200"
+              [style.width.%]="updater.progress()"
+            ></span>
+          }
+          <span class="relative flex items-center gap-1.5">
+            @switch (updater.state()) {
+              @case ('available') {
+                <ng-icon name="mynaDownload" size=".8rem" />{{ i18n.t('tabBar.update') }}
+              }
+              @case ('downloading') {
+                <ng-icon name="mynaSpinner" size=".8rem" class="animate-spin" />{{ i18n.t('tabBar.updating') }} {{ updater.progress() }}%
+              }
+              @case ('ready') {
+                <ng-icon name="mynaRefresh" size=".8rem" />{{ i18n.t('tabBar.restartToUpdate') }}
+              }
+            }
+          </span>
+        </button>
+      }
+
       <!-- connection manager (own native window) -->
       <button
         (click)="openManager()"
@@ -395,6 +427,7 @@ export class TabBar {
   readonly panels = inject(PanelsService);
   readonly settings = inject(SettingsService);
   readonly i18n = inject(I18nService);
+  readonly updater = inject(UpdaterService);
   private readonly rpc = inject(RpcService);
   readonly settingsOpen = signal(false);
   readonly localeOptions = SUPPORTED;
@@ -445,6 +478,13 @@ export class TabBar {
     void this.rpc.request.openConnectionManager({});
   }
 
+  /** Update pill: first click downloads, second click (when ready) applies + relaunches. */
+  onUpdateClick(): void {
+    const state = this.updater.state();
+    if (state === 'available') void this.updater.download();
+    else if (state === 'ready') this.updater.apply();
+  }
+
   showAbout(): void {
     void this.rpc.request.showAbout({});
   }