feat: expose /metrics endpoint and add telemetry ClickHouse credentials

.env.example

@@ -1,3 +1,9 @@
 WEB_PORT=5173
 API_PORT=3000
 DATABASE_URL=postgres://postgres:postgres@localhost:5432/zeavis_edu
+
+# ── Telemetry / ClickHouse ──────────────────────────────────────────
+# These credentials are used by the telemetry Docker Compose stack.
+# See telemetry/deploy/.env.example for production overrides.
+CLICKHOUSE_USER=telemetry
+CLICKHOUSE_PASSWORD=telemetry