feat(license): add BSL license enforcement with device limit indicator

- Add LICENSE_DEVICES env var (default 250, matches BSL 1.1 free tier)
- Add /api/settings/license endpoint returning device count vs limit
- Header shows flashing red "502/500 licensed" badge when over limit
- About page shows license tier, device count, and over-limit warning
- Nothing is crippled — all features work regardless of device count
- Bump version to 9.7.1

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

backend/app/config.py

@@ -135,9 +135,13 @@ class Settings(BaseSettings):
     # Retention cleanup — delete config snapshots older than N days
     CONFIG_RETENTION_DAYS: int = 90
 
+    # Licensing — BSL 1.1 free tier allows up to 250 devices.
+    # Commercial license required above this limit. Set to 0 for unlimited.
+    LICENSE_DEVICES: int = 250
+
     # App settings
     APP_NAME: str = "TOD - The Other Dude"
-    APP_VERSION: str = "9.7.0"
+    APP_VERSION: str = "9.7.1"
     DEBUG: bool = False
 
     @field_validator("CREDENTIAL_ENCRYPTION_KEY")