chore(desktop): add env files for dev/production and update dev scripts

- Track .env.development and .env.production for desktop app
- Add MAIN_VITE_API_URL to all env files
- Remove hardcoded GATEWAY_URL from dev scripts (now in .env.development)
- Update .env.example with full documentation of all env vars

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -16,6 +16,8 @@ release
 # env
 .env*
 !.env.example
+!apps/desktop/.env.production
+!apps/desktop/.env.development
 
 # platform specific
 *.dmg