🐛 fix(desktop): pin electron-builder to 26.14.0 to fix broken macOS update signing (#15527)

electron-builder was floating on `^26.8.1` and the repo commits no lockfile,
so each CI build resolved a fresh version. The canary.12 build (2026-06-07)
picked up 26.15.0, which regressed macOS .app bundle signing: codesign reports
"bundle format is ambiguous (could be app or framework)" and Squirrel.Mac
rejects the update during code-signature validation, so the app never quits
to install — surfacing as "auto-update does nothing".

26.15.0 introduced the two suspect changes (mac signing rework #9822 and the
full app-builder-bin Go→TS replacement #9829). 26.14.0 predates both and does
not touch macOS app-bundle signing/layout. Pinning the exact version cascades
to app-builder-lib / dmg-builder / builder-util (electron-builder pins those
exactly), stopping the toolchain from floating across CI installs.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

apps/desktop/package.json

@@ -78,7 +78,7 @@
     "cross-env": "^10.1.0",
     "diff": "^8.0.4",
     "electron": "41.3.0",
-    "electron-builder": "^26.8.1",
+    "electron-builder": "26.14.0",
     "electron-devtools-installer": "4.0.0",
     "electron-is": "^3.0.0",
     "electron-store": "^8.2.0",