feat(06-01): add config-history endpoint with RBAC and main.py registration

- GET /api/tenants/{tid}/devices/{did}/config-history endpoint
- Viewer+ RBAC with config:read scope
- Pagination via limit/offset query params (defaults 50/0)
- Router registered in main.py

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -281,6 +281,7 @@ def create_app() -> FastAPI:
     from app.routers.sse import router as sse_router
     from app.routers.config_backups import router as config_router
     from app.routers.config_editor import router as config_editor_router
+    from app.routers.config_history import router as config_history_router
     from app.routers.device_groups import router as device_groups_router
     from app.routers.device_tags import router as device_tags_router
     from app.routers.devices import router as devices_router
@@ -311,6 +312,7 @@ def create_app() -> FastAPI:
     app.include_router(device_tags_router, prefix="/api")
     app.include_router(metrics_router, prefix="/api")
     app.include_router(config_router, prefix="/api")
+    app.include_router(config_history_router, prefix="/api")
     app.include_router(firmware_router, prefix="/api")
     app.include_router(alerts_router, prefix="/api")
     app.include_router(config_editor_router, prefix="/api")