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/app/tasks/celery_app.py

@@ -4,7 +4,7 @@ from app.core.config import get_settings
 settings = get_settings()
 
 celery_app = Celery(
-    "tianpu_ems",
+    "ems_platform",
     broker=settings.REDIS_URL,
     backend=settings.REDIS_URL,
 )