chore: set electron AppImage dev kebab as committed default

src-electron/package.json desktopName and src-electron/electron-builder.yml
productName were committed as the prod kebab (`phoenix-code`), but the
matching display productName ("Phoenix Code Experimental Build") and
config.json `stage: dev` are dev defaults. Align both to the dev kebab so
a raw `npm run build:appimage` (no wrapper script) produces a coherent
dev AppImage; CI wrappers continue to overwrite per stage via
patchElectronStageBranding.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: abose

src-electron/electron-builder.yml

@@ -1,5 +1,5 @@
 appId: io.phcode.dev
-productName: phoenix-code
+productName: phoenix-code-experimental-build
 copyright: Copyright © 2024 phcode.dev
 
 asar: true

src-electron/package.json

@@ -8,7 +8,7 @@
   ],
   "version": "5.1.8",
   "productName": "Phoenix Code Experimental Build",
-  "desktopName": "phoenix-code",
+  "desktopName": "phoenix-code-experimental-build",
   "description": "Phoenix Code Experimental Build",
   "main": "main.js",
   "scripts": {