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>

src/bun/rpc-handlers.ts

@@ -1,4 +1,4 @@
-import { BrowserView, Utils } from "electrobun/bun";
+import { BrowserView, Updater, Utils } from "electrobun/bun";
 import type { AppRPC, EditorOpenContext } from "../shared/rpc";
 import { effectiveConcurrency, type AppSettings, type Result } from "../shared/types";
 import type { PanelContextMenu } from "./context-menu";
@@ -322,6 +322,25 @@ export function createAppRPC({
 					}),
 
 				listDrives: () => wrap(async () => ({ drives: listLocalDrives() })),
+
+				// ---- auto-updater ----
+				checkForUpdate: () =>
+					wrap(async () => {
+						const r = await Updater.checkForUpdate();
+						return { updateAvailable: r.updateAvailable, version: r.version };
+					}),
+
+				downloadUpdate: () =>
+					wrap(async () => {
+						await Updater.downloadUpdate();
+						return {};
+					}),
+
+				applyUpdate: () =>
+					wrap(async () => {
+						await Updater.applyUpdate(); // relaunches + quits; may never resolve
+						return {};
+					}),
 			},
 		},
 	});