Load the instance creation timestamp from data/labels/instance_id.json
(backfilling+persisting it for instances created before the field existed),
expose it as constants.instance_create_ts, and include it in the heartbeat
payload so Space can anchor Time-To-Value / onboarding analytics on real
install time rather than first-heartbeat.
Verified: py_compile, ruff, pytest tests/unit_tests/telemetry/ (37 passed).
b7d8332cb0