feat: disable native git poller by default — manual builds only
Set NATIVE_POLL_INTERVAL_MS=0 (default) to disable auto-polling.
Builds are triggered manually via POST /native-build with admin key.
Set NATIVE_POLL_INTERVAL_MS=60000 to re-enable polling.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>