feat(electron): auto-update via electron-updater + GitHub Releases

Phase 1 step 7 of VNCprodbuild. electron/main.ts calls
autoUpdater.checkForUpdatesAndNotify() once the app is ready, only for
packaged builds (app.isPackaged) - dev/test runs have no latest.yml and
would just log a noisy 404 on every launch. electron-builder.config.js gets
a matching `publish` block pointing at this repo's own GitHub Releases
(brvncde-dotcom/vncmail-plus) - the skill's recommendation over standing up
a new distribution channel, since the repo is already private. Flagged as
the "light decision" the skill calls it, not blocking.

Deliberately defensive: no code signing yet (step 9), so update
verification can fail on macOS in particular. Wrapped in try/catch +
autoUpdater's "error" event so a failed check is logged and swallowed, never
fatal - this is background maintenance, not something the user should be
blocked on.

Verified with a --dir packaged build: checkForUpdatesAndNotify() throws
ENOENT for app-update.yml (expected - that file is only emitted by a full
`electron-builder build`, not --dir) and the error handling swallows it
cleanly; the standalone server still boots and serves the app normally.
npm run test:electron still green (4/4) - autoUpdater is a no-op in the
unpacked dev/test path this suite exercises.

electron-builder.config.js

@@ -3,8 +3,8 @@
 // Phase 1 of the VNCprodbuild rollout (~/.claude/skills/VNCprodbuild/SKILL.md):
 //   step 1 - base config, no targets (superseded by this file)
 //   step 6 - this file: real packaging targets + branding icon (below)
-//   step 7 - electron-updater wiring (GitHub Releases feed) - adds a
-//            `publish` block on top of this file in a later commit.
+//   step 7 - this file's `publish` block + electron/main.ts's
+//            setupAutoUpdater() - electron-updater against GitHub Releases.
 //   step 9 - still open: code signing / notarization (Apple Developer ID,
 //            optional Windows cert) - both are human-owned purchases, not
 //            configured here. Builds below ship UNSIGNED.
@@ -79,4 +79,16 @@ module.exports = {
     ],
     category: "Network;Email;",
   },
+  // electron-updater feed (see electron/main.ts's setupAutoUpdater()).
+  // GitHub Releases, not a new distribution channel - the skill's
+  // recommendation since this repo is already private and this needs no
+  // extra infrastructure. "Light decision" per VNCprodbuild step 7, not
+  // blocking, but flagged: switching later (e.g. to a self-hosted update
+  // server) would mean revisiting this block and the `provider` electron-
+  // updater talks to.
+  publish: {
+    provider: "github",
+    owner: "brvncde-dotcom",
+    repo: "vncmail-plus",
+  },
 };