feat!: generic defaults, dashboard fallback, PV filter fix (v1.3.0)

- Replace all hardcoded Tianpu/天普 defaults with generic "EMS Platform"
- Add energy_today fallback: query raw energy_data when daily summary empty
- Fix PV device filter to include sungrow_inverter device type
- Update APP_NAME, CUSTOMER default, SECRET_KEY, SMTP, Celery, email templates

BREAKING: CUSTOMER default changed from "tianpu" to "default"
Existing deployments with CUSTOMER=tianpu in .env are unaffected.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/alembic.ini

@@ -1,6 +1,6 @@
 [alembic]
 script_location = alembic
-sqlalchemy.url = postgresql://tianpu:tianpu2026@localhost:5432/tianpu_ems
+sqlalchemy.url = postgresql://ems:ems2026@localhost:5432/ems
 
 [loggers]
 keys = root,sqlalchemy,alembic