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>

electrobun.config.ts

@@ -7,6 +7,14 @@ export default {
 		identifier: BRANDING.identifier,
 		version: BRANDING.version,
 	},
+	// Auto-updater feed. The flat artifacts land under /dl on the host (see site/);
+	// miniscp.com is fronted by an external proxy for TLS. baseUrl is baked into
+	// version.json at build time, so only builds made after this takes effect check
+	// for updates. generatePatch (default true) needs build-time network to this URL
+	// to diff against the currently-published version.
+	release: {
+		baseUrl: "https://miniscp.com/dl",
+	},
 	build: {
 		bun: {
 			entrypoint: "src/bun/index.ts",