Bake Sunshine remote admin + add one-command configured ISO builder

- Sunshine flatpak in first-boot list; autostarts with the console
  account's session (bc250-sunshine-autostart, honors CONSOLE_KID_USER)
- bc250-personalize: one-shot display names from /etc/bc250-console.conf
- build-console.sh + console.env(.example): fill in usernames/passwords/
  display names, get a fully personalized ISO — no post-install steps
  beyond per-account logins. Generated files git-ignored (credentials)
- Docs: Moonlight is the remote-admin path; RDP marked blocked by the
  mutter cursor-metadata screencast crash on GFX1013

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitignore

@@ -3,3 +3,8 @@ __pycache__/
 release-preview/
 /.bluebuild-scripts_*
 /Containerfile
+
+# build-console.sh generated files (contain credentials/machine-specific)
+/console.env
+/iso-config.generated.toml
+/files/console/etc/bc250-console.conf