feat(sofiia-console): expose /metrics and add basic ops counters

Expose Prometheus-style metrics endpoint and add counters for send requests, idempotency replays, and cursor pagination calls, including a safe in-process fallback exposition when prometheus_client is unavailable.

Made-with: Cursor

tests/test_sofiia_metrics.py

@@ -0,0 +1,11 @@
+from __future__ import annotations
+
+
+def test_metrics_endpoint_exposes_sofiia_counters(sofiia_client):
+    r = sofiia_client.get("/metrics")
+    assert r.status_code == 200, r.text
+    body = r.text
+    assert "sofiia_send_requests_total" in body
+    assert "sofiia_idempotency_replays_total" in body
+    assert "sofiia_cursor_requests_total" in body
+