Initial commit: astrape-ems split out of the combined Astrape tree

Everything that talks to the energy backend: the Sigenergy Modbus
client, its register map, the plant store, and the polling daemon.

Sits at the base of the Astrape dependency chain, because the plant
store is what satisfies gibil's PlantHistoryPort -- the oracle cannot
forecast without observed plant history. EnvLoader lives here for the
same reason: it is the only place all three repos can see it without a
fourth repo for 37 lines.

EnvLoader no longer resolves env/ from __file__. Where a package is
installed says nothing about where the deployment keeps its secrets;
it now uses the working directory, or ASTRAPE_ENV_DIR.

Extracted from a single repository where the forecasting engine, the
database plumbing, the hardware client, the ingest daemons and the web
UI all imported each other freely. Verified that every module imports
with gibil resolved from its own installed checkout.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,5 @@
+__pycache__/
+*.py[cod]
+*.egg-info/
+build/
+dist/