Add brain memory services and APIs

Introduce the backend pieces for brain memory ingestion, routing, and
system telemetry so the new knowledge workflows can project data into a
brain view. The supporting tests lock in the new behavior and keep the
expanded backend surface stable.

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

backend/app/services/system_service.py

@@ -0,0 +1,27 @@
+from datetime import datetime, UTC
+
+try:
+    import psutil
+except ModuleNotFoundError:  # pragma: no cover - optional runtime dependency fallback
+    psutil = None
+
+
+class SystemService:
+    def get_status(self) -> dict:
+        if psutil is None:
+            return {
+                'cpu_percent': 0.0,
+                'memory_percent': 0.0,
+                'disk_percent': 0.0,
+                'timestamp': datetime.now(UTC).isoformat(),
+            }
+
+        cpu_percent = psutil.cpu_percent(interval=None)
+        memory = psutil.virtual_memory()
+        disk = psutil.disk_usage('/')
+        return {
+            'cpu_percent': round(cpu_percent, 1),
+            'memory_percent': round(memory.percent, 1),
+            'disk_percent': round(disk.percent, 1),
+            'timestamp': datetime.now(UTC).isoformat(),
+        }