feat: image version identity + DB-config parity for nightly scripts

Version: CI now tags images YYYY.MM.DD-<shortsha> alongside :latest/:sha
and passes GIT_SHA/BUILD_TAG build-args; the running app reports them via
dashboard /api/health and admin /api/status (TrueNAS custom apps only show
'custom/1.0.0', so the app self-reports what it actually runs).

Config parity: every scheduler-run script (nightly_tune, eod_replay,
premarket_eval, regime, market_context, experiments cli) now loads
config_overrides at startup like the live services do — a bare env would
replay under DEFAULT exits (the documented 4.5x-baseline landmine).

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

tests/unit/test_env_overrides_db.py

@@ -29,6 +29,7 @@ def test_read_missing_table_is_empty(con):
 
 
 def test_load_db_applies_onto_environ(con, monkeypatch):
+    monkeypatch.setenv("ENV_OVERRIDES_DB", "1")   # force on (harness may disable)
     env_overrides.write_db_overrides({"TRADING_TEST_KNOB_XYZ": "42"}, con=con)
     monkeypatch.setattr(env_overrides, "_db_con", lambda: con)
     monkeypatch.setenv("TRADING_TEST_KNOB_XYZ", "1")   # compose value loses