Build tooling improvements for 4.1.4

- Rename flash-pi.sh → flash-stock-img.sh for clarity
- Add 16GB partition sizing option (faster imaging)
- Disable Pi OS auto-expand to preserve partition size
- Add pip-audit security check to release validation
- Add config.json.example, gitignore actual config

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/config.json.example

@@ -0,0 +1,12 @@
+{
+  "hostname": "stegasoo",
+  "username": "admin",
+  "password": "stegasoo",
+  "wifiSSID": "YourNetworkName",
+  "wifiPassword": "YourWiFiPassword",
+  "wifiCountry": "US",
+  "locale": "en_US.UTF-8",
+  "keyboardLayout": "us",
+  "timezone": "America/New_York",
+  "enableSSH": true
+}